4. The body next breaks up into a number of smaller bodies known as

_initial corpuscles_. These, in their turn, divide by simple division (in the manner already described) into numerous elementary bodies (fig. 119). Thus, the life-cycle is completed. The Chlamydozoa are, then, the minute granules inside the body of the _Cytoryctes variolæ_ or the _Neuroryctes hydrophobiæ_, so that the whole body of the _Cytoryctes_ or _Neuroryctes_ corresponds to the mantle and parasite of the Chlamydozoön. The Cytoryctes group is said to cause destruction of the host cell. The Cytoöikon group (_e.g._, trachoma bodies) causes proliferation of the host cell. In September, 1913, Noguchi[252] described the cultivation of the parasite of rabies in an artificial medium, similar to that used by him for the cultivation of _Spirochæta recurrentis_. The cultures were stated to be infective to dogs, rabbits and guinea-pigs. Levaditi, in December, 1913, stated that he had succeeded in cultivating spinal ganglia of rabid monkeys in monkey plasma. [252] _Journ. Exptl. Med._, xviii, p. 314. Noguchi and Cohen (November, 1913)[253] have succeeded in cultivating the so-called trachoma bodies, or at any rate bodies very closely resembling them morphologically. The medium employed was Noguchi’s ascitic fluid and rabbit kidney medium, as used for spirochætes. The coarser cultural forms stained blue with Giemsa’s solution, the finer ones stained red. Attempts to infect monkeys from the culture tubes failed. [253] _Idem_, p. 572. From their behaviour on treatment with such reagents as saponin, bile and sodium taurocholate, Prowazek considers that the Chlamydozoa approach the Protozoa. * * * * * PROTOZOA INCERTÆ SEDIS. *Sergentella hominis*, Brumpt, 1910. Et. and Ed. Sergent in 1908 found vermiform bodies about 40 µ long by 1 µ to 1·5 µ broad in the blood of an Algerian suffering from nausea and cold sweats, without other symptoms. The bodies were pointed at each end, with a somewhat ill-defined nucleus in the middle. Their systematic position is doubtful. ----------------------------------------------------------------- |NOTE.--An Appendix on Protozoology will be found on pp. 733–752. | |This has been prepared in order to incorporate a number of new | |additions to knowledge made since the body of the book was | |printed off. | ----------------------------------------------------------------- B. *PLATYHELMINTHES*, or Flat Worms. BY J. W. W. STEPHENS, M.D., B.C., D.P.H. DEFINITION: Bilaterally symmetrical animals without limbs, the form of which is leaf or tape-like, rarely cylindrical, and whose primary body cavity (segmentation cavity) is absent, the cavity being filled by a mesenchymatous tissue (parenchyma). The mouth is either situated at the anterior end of the body, or is shifted more or less backwards on to the flat ventral surface. The alimentary canal consists of a short fore-gut, which is frequently provided with a muscular pharynx, and of a simple forked or branched mid-gut; there is neither a hind-gut nor an anus; in one class, the Cestodes, the alimentary canal has entirely disappeared except for muscular remnants in the scolex. The INTEGUMENT OF THE BODY consists either of a ciliated epithelium of only one layer (Turbellaria), or of a cuticle and gland-like cells embedded in the parenchyma, or subcuticular layer (Cestodes, Trematodes). The dermo-muscular layer consists of annular, longitudinal, and even diagonal fibres, while the parenchyma is traversed by dorso-ventral fibres. The central NERVOUS SYSTEM, which is embedded in the parenchyma of the body, consists of cerebral ganglia, united together in the shape of dumb-bells, and of two or more longitudinal MEDULLARY FASCICLES, often forming transverse anastomoses. Organs of sense usually occur only in the free-living species, more rarely during the free-living stages of a few parasitic species and in a few ectoparasitic forms. [In Platyhelminthes simple eye-spots frequently occur, and in a few an auditory vesicle.] BLOOD-VESSELS and definite RESPIRATORY ORGANS are lacking [except in _Nemertinea_]; the EXCRETORY APPARATUS (formerly termed water-vascular system) is typical of the entire class. It commences in the interstices of the parenchyma, with peculiar terminal cells (ciliated funnels), which will be described later (p. 219), the capillary processes of which go on uniting into larger branches, and finally form two large collecting vessels, which, sometimes separately and sometimes united, open to the exterior through one, two, or numerous pores. Nearly all the Platyhelminthes are HERMAPHRODITIC, and in nearly all there are, in addition to the ovaries producing ova, other glands attached to the female genital apparatus, namely, the vitellaria or yolk glands, which provide a substance termed yolk, which serves as nourishment for the embryo. The fully formed eggs have shells and are “compound,” _i.e._, composed of the egg or ovarian cell, which is surrounded by numerous yolk cells or their products of disintegration. The two sexual openings usually lie close together, frequently in the fundus of a genital atrium; they are rarely separated from one another. Shell glands also usually occur (p. 221). Reproduction is sexual, often, however, combined with asexual methods of propagation (segmentation, budding). The Platyhelminthes live partly free in fresh or salt water, exceptionally also on land. The greater part, however, live as parasites on or in animals. CLASSIFICATION OF THE PLATYHELMINTHES. _Class I._--*Turbellaria* (or Eddy Worms). Flat worms for the most part, free living, and always covered with a ciliated epithelium. _Order 1._--_Rhabdocœlida_, gut unbranched. _Order 2._--_Tricladida_, gut with three main branches. _Order 3._--_Polycladida_, a central gut with lateral cæca. Development direct or through metamorphosis. They live in fresh and salt water or on land; very seldom as parasites. _Class II._--*Trematoda* (Sucking Worms[254]). [Usually known as Flukes.--F. V. T.] Flat worms, living as ecto- or endoparasites, that are only ciliated in the larval condition, and in their adult state are covered with a cuticle, the matrix cells of which lie in the parenchyma. They have either one, a few, or several suckers,[255] and frequently also possess chitinous fixation and adhesive organs. The intestine is single, but generally bifurcated, and not uncommonly there are transverse anastomoses between the forks or diverticula on them. Excretory organs double, with two orifices at the anterior extremity or a single one at the posterior end. Development takes place by a metamorphosis or alternation of generations (p. 283). These worms are almost always hermaphroditic, with two or more female and one male sexual orifice. They live, almost without exception, as parasites on vertebrate animals, but the intermediate generations are passed in molluscs. [254] This grouping goes back to the year 1800, and was made by J. G. H. Zeder, a physician and helminthologist of Forchheim, who divided the helminths, which until 1851 were generally regarded as a special class of animals, into the groups of round, hook, sucker, tape and bladder worms, as which they are recognized up to the present time. In 1809, K. A. Rudolphi gave them the names _Nematodes_, _Acanthocephali_, _Trematodes_, _Cestodes_ and _Cystici_. [255] A sucker or acetabulum (little cup) is a round, cup-shaped muscular organ, the muscles of which are _sharply defined_ from those of the body. _Class III._--*Cestoda* (Tapeworms). Endoparasitic flat worms without an alimentary canal. The larval stages are rarely ciliated, but are usually provided with six spines; the adult worm is covered with a cuticle, the matrix cells of which are embedded in the parenchyma. The body consists of a single segment (Cestodaria) or a chain of segments, in which case it consists of the scolex and the segments containing the sexual organs (proglottides) (Cestodes s. str.). The scolex is provided with various adhesive and fixation organs, and there are calcareous corpuscles in the parenchyma. Excretory organs symmetrical, opening at the posterior end. These worms are always hermaphroditic, and then possess one or two female and one male sexual orifice. During development a larval intermediate stage (“measle”) occurs and almost always in a different host to that in which the adult sexual worm lives. The adult stage is parasitic in vertebrate animals; but the larval stage may occur in invertebrates. Class II. *TREMATODA*, Rud. These worms are usually leaf- or tongue-shaped, but also barrel-shaped or conical; they vary from 0·1 mm. to almost 1 m.[256] in length; most of them, however, are small (5 mm. to 15 mm.). The surface on which the orifice of the uterus and the male sexual opening are situated is termed the ventral surface; the oral aperture, which also acts as anus, is always at the anterior end in the sub-order _Prostomata_ (p. 230), but in the sub-order _Gasterostomata_ it is ventral. [256] _Nematobothrium filarina_, van Bened., on the branchial chamber of the Tunny. Suckers are always present and occur in varying numbers and positions at the anterior extremities as well as on the ventral surface, and occasionally on the lateral margin and on the dorsum; the beginning of the intestine (mouth) is always surrounded by a sucker in the _Prostomata_. In or near the suckers there may be chitinous hooks, claws or claspers, or the surface of the body is more or less covered with spines, scales or prickles; in one genus (_Rhopalias_) there are projectile tentacles beset with spines on the sides of the anterior part of the body. The body of adult Trematodes is covered by a homogeneous layer of varying thickness, which either lies directly over the external layer (basement membrane) of the parenchyma, or over the muscles embedded in the parenchyma. This investing membrane (cuticle) arises from pear-shaped or spindle-shaped cells arranged singly or in groups (which lie between or internal to the diagonal muscles), and is connected with them by processes; these cells one may regard as epithelial cells which have sunk down, or possibly as parenchymatous cells. An epithelium of one layer is also found on the body of young stages, but it disappears during growth, and only occasionally do its nuclei persist until adult life. In its place we then find the cuticle, which, moreover, extends into all the body openings more or less deeply. It is thus a debatable point whether the “investing layer” of flukes is a cuticle--that is, consists of modified epithelial cells--or whether it is a basement membrane, _i.e._, compressed and modified connective tissue cells; in this latter case the true epidermis and cuticle have been cast off. In the former case the epidermal cells are the pear-shaped cells referred to above. According to recent authors it consists of two parts, an outer true cuticle and an inner basement membrane. There are also unicellular cuticular glands, lying isolated or in groups, which are termed cephalic, abdominal, or dorsal glands according to the position of their orifice. The PARENCHYMA is a connective substance, the structure of which is still a matter of dispute. It consists, according to some authors, of multipolar cells, the offshoots from which anastomose with each other so that a network, permeating the entire body and encompassing all the organs, is produced. There exists also, as part of it, a homogeneous matrix, in the form of lamellæ and trabeculæ that border small cavities communicating with each other and filled with fluid. According to other authors, the parenchyma of the Trematodes consisted originally of cells, of which, however, only the cell membranes remain, while the protoplasm has been liquefied except for small residua around the nucleus. Between these cells an intercellular mass has appeared. By partial absorption of the walls, adjoining spaces unite, and the originally flat cell walls become transformed into trabeculæ. According to this view the cavities filled with fluid are _intra_-cellular, according to the former view _inter_-cellular. Pigment cells occur only in a few species. The MUSCULAR SYSTEM of the Trematodes is composed of (1) a dermo-muscular tube, (2) the dorso-ventral or parenchymal muscles, (3) the suckers, and (4) the special muscles of certain organs. The dermo-muscular tube, which lies fairly close to the cuticle, consists of annular, diagonal, and longitudinal fibres which surround the entire body in one or several layers, and as a rule are more strongly developed on the ventral surface as well as in the anterior part of the body. The MUSCLES OF THE PARENCHYMA are found chiefly in the lateral parts of the body and pass through the parenchyma in a dorso-ventral direction; their diverging brush-like ends are inserted on the inner surface of the cuticle (fig. 120). [Illustration: FIG. 120.--Half of a transverse section through _Fasciola hepatica_, L. 25/1. _Cu._, Cuticle with scales; under the cuticle are circular muscles, and adjoining them the longitudinal and diagonal muscles; internal to the latter are the matrix cells of the cuticle; _I._, gut; the other similarly contoured cavities are gut diverticula that have been transversely or obliquely sectioned; _F.v.s._, vitellaria; _Ex.v._, excretory vessels; _T._, testes; _Md._, median plane; the fibres passing from the ventral to the dorsal surface are the muscles of the parenchyma. The parenchyma itself is omitted.] The suckers are specially differentiated parts of the dermo-muscular tube. Their concave inner surface is lined by the continuation of the cuticle and their convex external surface is covered by a more dense tissue that frequently takes the form of a refractive membrane, thus separating them from the parenchymal muscles. The principal mass of the suckers consists of muscular fibres which run in three directions--equatorial, meridional and radial. The equatorial fibres correspond to the annular muscles, the meridional fibres to the longitudinal muscles, and the radial fibres to the muscles of the parenchyma; the radial fibres are always the most strongly developed. The function of these muscles is evident from their position; the meridional fibres flatten the suctorial disc and diminish the depth of its cavity, so that the internal surface may adhere to the object to be held; if the equatorial fibres now contract, the sucker rises by elongating longitudinally, and its inner surface is drawn in by the contraction of the radial muscles. Thus the sucking disc becomes adherent. Usually also there is a sphincter at the border of the suckers, which plays its part during the act of adhesion by constricting in a circular manner that part of the mucous membrane to which it is attached. The loosening of the fixed sucker is effected by relaxation chiefly of the radial fibres, by the contraction of the meridional fibres and certain bundles of muscles situated at the base and at the periphery of the suckers. The connective and elastic tissues between the muscles of the suckers probably also take part in the process. [Illustration: FIG. 121.--_Harmostomum leptostomum_, Olss., an immature specimen from _Helix hortensis_. _Nervous system_, according to Bettendorf. _A.s._, ventral sucker; _C.g._, cerebral ganglion; _Ex.p._, excretory pore; _G.p._, genital pore; _O.s._, oral sucker; _M.d._, dorsal medullary nerve; _M.l._, lateral medullary nerve; _N.ph._, pharyngeal nerve; _M.v._, ventral medullary nerve. Magnified.] Of the muscles of the organs which have developed from the parenchyma muscles we may briefly mention those bundles that are attached to certain parts of the genital apparatus, to the suckers, to the hooks and claws, and also, at all events in _Fasciola hepatica_, to the spines. The sheaths used for the projection of the tentacles of the _Rhopaliadæ_ are also muscular. The contractile elements consist of fibres of various lengths that are mostly parallel to one another, and frequently anastomose; a cortical substance finely fibrillated can usually be distinguished from an internal homogeneous mass; large nucleated cells of uniform size are always connected with them; these have been variously interpreted, but have been proved to be myoblasts, one or more of their processes constituting the muscular fibres. The MOVEMENTS of the Trematodes consist in alterations of form and position of the body, as well as in creeping movements. In the NERVOUS SYSTEM (fig. 121) can be distinguished a cerebral portion as well as strands (medullary strands) running from it, and peripheral nerves. The cerebral portion always consists of two large ganglia situated in the anterior end of the body which pass dorsally over the œsophagus and are connected by means of a broad and thick commissure composed of fibres only. From each ganglion three nerves run anteriorly--the inner and dorsal nerve for supplying the anterior dorsal part of the body; the median and ventral for the oral sucker; and the exterior and lateral likewise for the supply of the sucker. In a similar manner three strands run backwards from each ganglion--one dorsal, one lateral and one ventral. The dorsal and ventral strands become united and curve backwards; the symmetrical lateral strands are connected by means of transverse commissures, the number of which vary according to the species. Such commissures also exist between the lateral and the two other strands on each side. There are ganglion cells along the entire course of the posterior cords, more particularly at the points of origin of the commissures. There also appears to be in addition a fourth anterior and posterior pair of nerves, the front pair for the oral sucker and the hind pair for the pharynx. The peripheral nerves, which spring from the posterior strands as well as from the commissures, either pass directly to the muscular fibres or to the sensory cells that are situated at the level of the subcuticular cells, or they reach these after the formation of a plexus situated immediately beneath the dermo-muscular layer; the processes directed outwards terminate in small vesicles in the cuticle. As to other ORGANS OF SENSE, simple eyes, two or four in number, are known in several ectoparasitic species as well as in a few free-living larval stages (Cercariæ) of endoparasitic forms. In the adult stage, however, they usually undergo complete atrophy. The ALIMENTARY CANAL commences with an oral aperture, generally terminal or sub-terminal (ventral) at the anterior extremity, which leads into an oral cavity usually surrounded by a sucker; the œsophagus, of various lengths, is directed backwards and is generally surrounded by a muscular pharynx (fig. 122). In some cases there exists between the sucker and pharynx, pharyngeal pouches (præpharynx). Sooner or later the intestine divides into two lateral branches directed backwards, both of which end blindly (cæca) at the same level.[257] In many ectoparasites (_Monogenea_ [p. 222]) a connection exists between the genital glands and one of the intestinal branches (ductus vitello-intestinalis [fig. 123]). [257] The following conditions represent deviations from this type: (1) In _Gasterostomum_ the oral aperture is situated in the middle of the ventral surface, and occasionally is even nearer to the posterior than to the anterior end. There is no proper oral sucker, but the pharynx is thus termed. (2) A few genera, such as _Gasterostomum_, _Aspidogaster_, _Diplozoon_, etc., have only _one_ intestinal diverticulum, which is undoubtedly to be taken as representing the primitive condition, as it is also often found in the young stages of the _Trematoda_. (3) The branches of the intestines are curved and united behind (several _Tristomidæ_ and _Monostomidæ_), while in _Polystomum integerrimum_ (in the bladder of frogs) there are several commissures between the intestinal branches, and in the _Schistosomidæ_ the united intestinal branches proceed as one channel towards the posterior end. (4) The termination of the two intestinal branches is not always on a level; they are therefore of different lengths. (5) When the œsophagus is very long the intestinal branches extend both forward and backward, so that the gut exhibits the form of an *H*. (6) In the broad and flat species the gut-forks form diverticula mostly externally but also internally; these again may branch (fig. 139). (7) In a few cases (_Nematobothrium_, _Didymozoon_) the intestine completely disappears up to the pharynx. The oral cavity, pharyngeal pouches, pharynx, and œsophagus are lined with a continuation of the cuticle of the body; the gut cæca are lined with tall cylindrical epithelium (fig. 120). The œsophagus and intestinal branches often have also one layer of annular and longitudinal muscles; the pharynx has essentially the structure of a sucker (fig. 122). [Illustration: FIG. 122.--Median section through the anterior part of _Fasciola hepatica_: the oral sucker, pharyngeal pouches, pharynx, œsophagus, cuticle with spines, and the body parenchyma.] The accessory organs of the alimentary canal consist of groups of unicellular SALIVARY GLANDS that discharge into the œsophagus in front of or behind the pharynx, or even into the pharynx itself. The food of the Trematodes consists of mucus, epithelial cells, the intestinal contents of the hosts, and often also of blood, and this not only in those species living in the vascular system, but also in species living as ectoparasites or in the intestine or biliary passages of their hosts. [Illustration: FIG. 123.--_Polystomum integerrimum_, a monogenetic fluke from the urinary bladder of the frog. _i._, intestine; _h._, large hooks of the sucking disc; _h.k._, smaller hooklets; _l.c.v._, longitudinal vitelline ducts; _o._, oral orifice; _Oot._, oötype; _ov._, ovary; _s.p._, suckers of the disc; _tr.c.v._, transverse vitelline ducts; _Ut._, uterus with ova; _v._, entrance to the vagina; _v.d.e._, vas deferens; _v.d.i._, ductus vitello-intestinalis; the vitellaria and testes are not shown. Magnified. (After Zeller.)] [Illustration: FIG. 124.--_Allocreadium isoporum_, Looss. Excretory apparatus. Of the other organs, the oral sucker, pharynx, genital pore, ventral sucker, ovary and testes are shown; the cylindrical excretory bladder is in the posterior end. 38/1. (After Looss.)] The final products of assimilation dissolved in the fluids of the body are distributed throughout the parenchyma and are thence expelled by a definite tubular system (excretory apparatus, proto-nephridia, formerly also termed the water-vascular system). This system, which is distributed throughout the entire body (fig. 124), is symmetrically developed, and, in the ectoparasitic Trematodes, it opens, right and left, at the anterior end on the dorsal surface; in all other flukes, however, it opens singly into the excretory pore (foramen caudale) at the centre of the posterior border; in those cases, however, where a sucker is present at the posterior end, as in the Amphistomata, the excretory pore is situated on the dorsal surface close in front of the sucker. The EXCRETORY SYSTEM[258] consists of several parts: (1) of the more or less numerous terminal “flame” cells or funnel cells (figs. 124, 125); (2) of the capillaries ending in them; (3) of larger vessels receiving the capillaries; and (4) of the excretory bladder. Terminal cells and capillaries may be compared to unicellular glands with long excretory ducts; the cellular body (fig. 125) is comparatively large, stretched longitudinally, more rarely transversely, and provided with numerous processes, that are lost in the parenchyma; within is a conical cavity (analogous to the secretory cavity of unicellular glands) which is continued directly into the structureless capillary; at its blind end is a bunch of cilia projecting into the cavity, and which, during life, shows a flickering motion (ciliary flame). The nucleus is situated in the protoplasm of the terminal cell at its blind end. [258] The following description relates in the main to the _Distomata_. The entire apparatus thus begins blindly--_i.e._, within the terminal cells, to which must be ascribed the capacity of taking up from the fluid that permeates the parenchyma the products which are first collected into their own cavities and thence excreted by means of the capillaries and vessels. [Illustration: FIG. 125.--Terminal flame cell of the excretory system. _n._, nucleus of cell; _c._, bundle of cilia forming the “flame”; _p._, processes of cell extending into parenchyma; _d._, excretory capillary. (Stephens.)] The vessels possess definite walls, consisting of a membrane and a nucleated protoplasmic layer. They unite at many points on either side, and again pass into other canals (COLLECTING TUBES), which finally, travelling towards the posterior end, discharge into the excretory bladder (fig. 124). The form and size of the bladder vary much according to the different species, but it always possesses its own flattened epithelium, surrounded by circular and longitudinal muscles, the circular muscles forming a sphincter around the opening. Frequently also the structure of the bladder extends to the tubules discharging into it, which therefore are not to be regarded as separate “vessels,” but rather as tubular diverticula of the bladder, directed anteriorly. In some few species the diverticula also branch and the branches anastomose, so that a network of tubules ensues which receives the vessels or capillaries. In such cases there are also ciliary tracts in the tubules. The contents of the entire apparatus usually consist of a clear or sometimes reddish fluid; in some species there are larger or smaller granules, and occasionally also concretions occur. [Illustration: FIG. 126.--Diagram of female genitalia. _Ov._, ovary; _ovd._, oviduct; _L.c._, Laurer’s canal; _Rec. sem._, receptaculum seminis; _Vit. R._, vitellarian reservoir; _t.v.d._, transverse vitelline duct; _Oo._, oötype; _Sh. gl._, shell gland; _Rec. ut._, receptaculum uterinum; _ut._, uterus. (The various parts are not to the same scale.) (Stephens.)] [Illustration: FIG. 127.--Diagram of male and part of female genitalia. _ut._, uterus; _vag._, vagina; ♀, opening of vagina; _g.s._, genital sinus; _g.p._, genital pore; ♂, opening of ejaculatory duct or vas deferens; _c.s._, cirrus sac; _c._, cirrus; _p.p._, pars prostatica; _s.v._, seminal vesicle; _e.j._, ejaculatory duct or vas deferens; _v.e._, vas efferens; _t._, testis. (Stephens.)] _Sexual Organs._--Nearly all the Trematodes are hermaphrodites, and only a few (_Schistosomidæ_, _Koellikeria_) are sexually differentiated. The sexual organs usually lie in the “central field” limited by the gut cæca; the vitellaria, on the other hand, are, as a rule, external to the gut cæca in the “lateral fields.” The male apparatus[259] is composed of two variously formed testes (fig. 127) (globular, oval, indented, lobed, or ramified), which may lie side by side or one behind the other; from each testicle a tube (vas efferens) originates; sooner or later, both tubes as a rule unite to form the ejaculatory duct or vas deferens, which is frequently enclosed in a muscular CIRRUS SAC, or more rarely passes directly into the genital pore. The cirrus, which is the thick muscular terminal portion of the vas deferens, can be everted and protruded from the cirrus sac and serves as an organ of copulation. The walls of the muscular portion of the tube (the cirrus) are attached to the walls of the cirrus sac, and hence when the sac contracts the cirrus cannot be protruded except by evagination of its lumen. Opening into the middle portion of the vas deferens, and as a rule enclosed in the cirrus sac, is found a mass of unicellular glands (prostate), the vesicula seminalis (which is likewise within, or may also be outside the sac) being the dilated first portion of the vas. [259] The following description relates mainly to the _Distomata_. The female genitalia (fig. 126) consist of an ovary, usually situated in front of the testes, the form of which varies according to the species, the usually double vitellaria, the ducts and a number of auxiliary organs; the short oviduct directed towards the centre arises from the ovary, and is connected in the median line with the excretory duct of the vitelline glands. These grape-like glands possess longitudinal excretory ducts, which assume a transverse direction behind the ovary, unite together at the median line and form a single duct, often dilated into a vitelline receptacle, that unites with the oviduct. Near this point, moreover, there frequently opens a canal (Laurer’s canal) which begins on the dorsal surface, and on the inner end of which a vesicle filled with sperm (receptaculum seminis) usually occurs (fig. 126). Moreover, there are also numerous radial unicellular glands (shell glands) at or beyond the point of junction of the oviduct, vitelline ducts and Laurer’s canal. In this portion of the duct (oötype), which is usually dilated, the ovarian cells are fertilized, surrounded with yolk cells and shell material, and as ova with shells they pass into the uterus (a direct continuation of the oviduct), which, with its many convolutions, occupies a larger or smaller portion of the central field, and runs either direct to the genital pore or, forming convolutions, first runs posteriorly and then bends forward (descending and ascending limbs). In both cases the terminal part lies beside the cirrus pouch and discharges beside the male orifice either on the surface of the body or into a genital atrium. The terminal portion of the uterus, which is often of a particular structure, serves as a vagina (METRATERM). The cirrus sac may include (1) the genital atrium (_i.e._, the common sinus, into which the vas deferens and vagina may open), or (2) a variable extent of the vas from cirrus to seminal vesicle. Thus the latter may be outside the sac. In the absence of a sac, the genital sinus may be surrounded by a pseudo-sucker, as in _Heterophyes_ (in some cases the ventral sucker itself, from its close proximity to the genital pore, serves as an accessory copulatory organ). In other cases copulatory organs are formed by hooks projecting into the lumen of the terminal portion of the vas. The GENITAL PORE, which is the opening from the genital sinus on to the surface, is generally situated at or near to the median line on the ventral surface and in the anterior region of the body; in most of the _Distomata_ it is in front of the ventral sucker, in other cases, _e.g._, in the _Cryptocotylinæ_, it is behind.[260] [260] The typical position of the genitalia is subject to many deviations, which are of importance in the differentiation of the genera and families. The following are some few of these deviations: (1) The genital pore remains on the ventral surface, but is situated beside or behind the ventral sucker, or it becomes marginal, and is then found in front of or beside the oral sucker, or at a lateral edge, or, finally, in the centre of the posterior border; the ducts also correspondingly alter their direction. (2) The ovary usually lies in front of the testes, not rarely, however, behind them or between them. (3) The three genital glands mostly lie together close in front of, or behind, the centre of the body; they may be moved far back, and may incidentally become separated one from the other. (4) The vitellarium may be single, in which case it then may lie in the central field. (5) A few forms possess but one, others several or numerous testes. Amongst the ectoparasitic trematodes there are also species with but one testis; but they mostly have several. As a rule, their uterus is short, but the oötype well developed. Special canals (vagina), single or double, are used for copulation, not the uterus. The vitelline ducts also communicate with the intestine through the canalis vitello-intestinalis (fig. 123). The spermatozoa do not differ essentially in their structure from those of other animals; the ovarian or egg cells are cells without integument and contain a large nucleus and a little protoplasm; the vitellaria also produce nucleated cells, in the plasm of which there are numerous yellow yolk granules; the yolk cells detach themselves, like the ovarian cells, from the ovarium, and pass into the oviduct to surround each ovarian cell in the oötype. They disintegrate sooner or later in the completely formed egg and are utilized as food by the developing embryo. DEVELOPMENT OF THE TREMATODES. (1) _Copulation._--Observation has demonstrated that the one or two vaginæ occurring in the ectoparasitic Trematodes are utilized as female organs of copulation, and that the copulation is cross; it is also known that Laurer’s canal, which was formerly generally regarded as the vagina, has only quite exceptionally, if at all, served the digenetic Trematodes as such--it appears to be homologous with the canalis vitello-intestinalis of the _Monogenea_[261]--but the terminal portion of the uterus, termed the metraterm, is used for copulation. Cross-copulation occurs as well as auto-copulation and auto-fecundation. The spermatozoa subsequently pass through the entire uterus, which is still quite short at the time the male organs are matured; the maturation of which, as usually is the case in hermaphrodites, precedes that of the female organs. It is only later with the onset of egg formation that the uterus is fully developed. Copulation, however, takes place also in the case of fully grown forms with completely developed uteri. [261] _Monogenea_: Trematoda in which the anterior sucker, if present, is double. Development without an intermediate host. [Illustration: FIG. 128.--Ovum of _Fasciola hepatica_, L., cut longitudinally. The lid has been lifted in the process. Within the egg are numerous yolk cells, and at the lid end there is the still unsegmented ovum (dark). 240/1.] [Illustration: FIG. 129.--Miracidium of _Fasciola hepatica_ that has just hatched from the egg, with a distinct cuticular ciliated epithelium. Magnified. (From Leuckart.)] (2) _Formation of the Ova._--The ovarian cells arising from the ovary first become mature after their entry into the oötype by the formation of three polar bodies, fertilization then taking place. At the same time as the ovarian cell a number of yolk cells from the vitellarium and secretion, drop by drop, from the shell gland reach the oötype.[262] The shell is then formed during the generally active contractions of the oötype walls and then passes on into the uterus. In the uterus of the endoparasitic trematodes the eggs accumulate more and more, often in large quantities, while in ectoparasitic species generally only one or some few eggs can be found. The completed ova are of various forms and sizes. They are mostly oval, at all events in the digenetic trematodes, and the yellowish or brown shell is provided with an opening at one pole which is closed by a watch-glass-shaped lid (operculum). Appendages (filaments) on the shell--at one or both poles--are uncommon, but are the rule in the ova of the _Monogenea_ (ectoparasitic species). [262] [Recent work (_e.g._, Goldschmidt, _Zool. Anzeiger_, xxxiv, p. 482) has shown that the older views regarding the formation of the egg must be modified. In certain species, at any rate, the shell material is formed by the yellow droplets of the yolk glands and not by the so-called shell gland (Mehli’s gland) secretion, which is clear and watery. The function of this secretion accordingly still requires explanation; according to Looss it serves as a covering secretion for the egg-shell proper. It appears also that other granules, the yolk granules as distinct from the shell drop granules, are not always used up during the development of the embryo and hence do not function as yolk, so these also when they exist, and frequently they are wanting, must serve some other purpose, possibly that of imbibing water for the use of the embryo.--J. W. W. S.] (3) _Deposition of the Ova._--Soon after their formation, the _Monogenea_ (ectoparasitic trematodes) deposit round the place of their attachment on the skin or the gills or other organs of their hosts, eggs which attach themselves by means of their filaments. The embryonic development thus takes place outside the parent. This also holds good for the eggs of many endoparasitic species, although as a rule in these the eggs are always retained for a longer time in the uterus. Moreover, they usually here undergo a part or a whole of their development, and are eventually deposited in those organs in which the adult forms are parasitic, but this is not always the case, as the egg, _e.g._, of _F. hepatica_ appears in bile (and fæces) quite unchanged. By the natural passages they eventually get out of the body, and in cases where such do not exist, as in the case of the blood-vessels, the eggs pass out by means of the kidneys. (4) _The embryonic development_, after irregular segmentation of the ovum into a number of blastomeres, leads to the formation of a solid blastosphere or morula, which is surrounded by a cellular investing membrane (yolk envelope), while the principal mass of the cells forms the embryo, which uses for its nourishment the yolk cells, which have in the meantime disintegrated (_cf._ footnote, p. 223). Usually, after the ova have reached water the embryos hatch out, leaving the yolk envelope in the egg-shell; in other cases, however, the embryos only hatch out after having been subjected to the influence of the intestinal juices, that is to say, in the intestine of an intermediate host which has ingested with its food the ova that have escaped from the primary host. (5) _The post-embryonic development_ of the Trematodes is accomplished in various ways; the process is the most simple in the ectoparasitic species (_Monogenea_), the young of which should certainly be regarded as larvæ, because they possess characteristics (cilia, simple gut, etc.) that are lacking in the adult worms, but which, nevertheless, pass into the adult state direct after a relatively simple metamorphosis. In the _Holostomata_,[263] a group found chiefly in the intestine of aquatic birds, and which rarely occur in other vertebrates, the ova develop in water. The young are ciliated all over, and, after having entered an intermediate host (leeches, molluscs, arthropods, amphibians, fishes) living in the water, they undergo a metamorphosis into a second larval stage; they then encyst and await transmission into the final host, where they become adult Metastatic trematodes, _i.e._, trematodes without asexually produced generations (p. 229). [263] _Holostomata_: Prostomata with (in addition to the oral and ventral suckers) a third fixation apparatus, generally on a separate part of the body. In the remaining so-called digenetic trematodes (p. 230) one or two asexual generations interpose between the miracidium and terminal stage, so that quite a number of adult worms may originate from one egg. Usually the young, which are termed MIRACIDIA[264] (fig. 129), hatch in water, where they move with the aid of their cilia. Sooner or later they penetrate into an intermediate host, which is always a snail or a mussel, and while certain of their organs disappear, they grow into a gutless germinal tube (SPOROCYST, fig. 131). These are simple elongated sacs with a central body cavity. They may or may not have excretory tubules. In these, according to the species, the larval stages (CERCARIÆ) that will ultimately become adult worms are produced, or another intermediate generation is first formed, _viz._, that of the REDIÆ[265] (figs. 132, 133), which are always provided with an intestine, and these then give rise to cercariæ (figs. 130, 134). The cercariæ, as a rule, leave their host and move about in the water with the assistance of their rudder-like tails. After a little time, however, they usually again invade an aquatic animal (worms, molluscs, arthropods, fishes, amphibians), then they lose their tails and become encysted (fig. 135); here they wait until they attain, together with their host, the suitable terminal host, and in this new situation they establish themselves and reach maturity. Or, again, the cercariæ may themselves encyst in water or on foreign bodies (plants) and wait until they are taken up directly by the terminal host, _e.g._, sheep. [264] [Also known as ciliated embryos.--F. V. T.] [265] [In _Fasciola hepatica_ in the summer months the rediæ give rise to daughter rediæ, which then give rise to cercariæ.--J. W. W. S.] [Illustration: FIG. 130.--A group of cercariæ of Echinostoma sp. (from fresh water). 25/1.] Accordingly the following conditions are necessary for the completion of the entire development: (1) The terminal host in which the adult stage lives; (2) an intermediate host into which the miracidia penetrate and in which they become sporocysts; (3) a second intermediate host in which the cercariæ become encysted. In certain species, as in _Fasciola hepatica_, this second host is omitted, as the cercariæ spontaneously encyst on plants, or again (in other species) encystment may occur within the first intermediate host, when, in fact, the cercariæ (which in this case do not acquire an oar-like tail) do not swarm out of, but encyst themselves within their sporocysts. The development, moreover, may be further complicated by rediæ appearing in addition to the sporocysts, though this occurs in the first intermediate host and not in a second one. Animals that harbour adult digenetic Trematodes thus become infected by ingesting encysted cercariæ, which either occur (1) in certain animals (second intermediate hosts) on which they feed, or (2) in water, or (3) on plants, or finally (4) in the first intermediate host; whereas animals harbouring encysted cercariæ have been directly infected by the corresponding tailed stage, and animals harbouring germinal tubes (sporocysts or rediæ) have been infected by the miracidia. [Illustration: FIG. 131.--Development of _Fasciola hepatica_, L. _a_, the miracidium in optical section showing cephalic lobe, X-shaped eye-spot resting on the cerebral ganglion, two germ balls; below each of these a flame cell, and still lower germ cells lying in a cavity (primitive body cavity). _b_, young sporocyst with two eye-spots, and germ balls; the cells lining the cavity are not shown. _c_, older sporocyst with a young redia. Magnified. (After Leuckart.)] Thus certain species of ducks and geese become infected with _Echinostoma echinatum_ by devouring certain water-snails (_Limnæus_, _Paludina_) in which the encysted cercariæ occur. Oxen become infected with _Paramphistomum cervi_ (= _Amphistomum conicum_) by swallowing with water, cysts of this species which occur at the bottom of puddles and pits. Sheep are infected with _Fasciola hepatica_ by eating grass to which the encysted cercariæ of the liver-fluke are attached; our song-birds infect themselves or their young with _Urogonimus macrostomus_ by tearing off pieces containing the corresponding sporocysts which are full of encysted cercariæ from snails (_Succinea amphibia_), which act as the first intermediate hosts, and eating, or offering their young these pieces. (1) The MIRACIDIA of the digenetic Trematodes are comparatively highly organized, and the mode of their formation from the segmentation cells of the ovum is only imperfectly known. They have a cuticular epithelium (fig. 129) entirely or partly covered with cilia, beneath this a dermo-muscular tube composed of circular and longitudinal muscles; also, a simple gut sac with an œsophagus, occasionally also with pharynx, salivary glands and boring spine, also a cerebral ganglion on which, in some species, there are eyes (fig. 131, _a_). As to the excretory organs, they are represented by two symmetrically placed terminal flame cells, with excretory vessels opening separately; there is a more or less ample (primary) body cavity between the parietes of the body and the gut; from the cellular parietal lining of this cavity single cells (germ cells) become free (fig. 131, _a_, _b_), and become rediæ or cercariæ. [The germ cells of the miracidium and the germ balls of the sporocyst arise, according to some observers, by further division of undifferentiated blastomeres; according to others from the cells of the lining wall of its body cavity. It is from these free germ balls that the redia stage is developed. [In the germ ball or morula appears an invagination, giving rise to the cup-shaped gastrula stage. This elongates and forms the REDIA (fig. 131, _c_). [In the interior of the redia cells are budded off and develop into gastrulæ, as in the case of the sporocyst. These become a fresh generation of rediæ or give rise to the third stage (CERCARIA).] [Illustration: FIG. 132.--Young redia of _Fasciola hepatica_, with pharynx and intestine, with a circular ridge anteriorly and a pair of processes posteriorly and masses of cells (germ balls) in the interior. Magnified. (From Leuckart.)] [Illustration: FIG. 133.--Older redia of _Distoma echinatum_, with rudimentary intestine _i._; cercariæ, _c._; germ balls, _b._; and birth pore, _g._ Magnified.] (2) The SPOROCYSTS, on the contrary, which are produced direct from the miracidia, are very simple, as all the organs of the latter disappear, even to the muscles and excretory organs, during or after penetration into the intermediate host, whereas the budded and still budding cells of the wall of the (primary) body cavity continue to develop rapidly and form germ balls. The sporocysts when fully developed have the appearance of tubes or fusiform bodies with rounded edge; they are frequently of a yellow colour. Their length rarely exceeds a few millimetres; in some species their size increases exceedingly through proliferation, and they then occupy a large portion of the body of the intermediate host. (3) The REDIÆ (figs. 132, 133), on the other hand, are more cylindrical and always have a simple intestine of varying length, provided with a pharynx; they likewise possess, situated near the circular ridge, a “birth pore” which serves for the exit of the cercariæ originating within them. [Illustration: FIG. 134.--Cercaria of _Fasciola hepatica_; the cutaneous glands at the side of the anterior body. Magnified. (After Leuckart.)] [Illustration: FIG. 135.--Encysted cercaria of _Fasciola hepatica_. Magnified. (After Leuckart.)] (4) The CERCARIÆ[266] are very different; typically they consist of the anterior body and the oar-like tail at the posterior end (fig. 134). The former, even to the genitalia, has the organization of the adult digenetic Trematodes, and thus allows the easy recognition of at least the characters of that large group to which the species in question belongs. On the other hand, however, there are also organs that are lacking in the adult form, such as, in many, the boring spine in the oral sucker, or the eyes situated on the cerebral ganglion; moreover, also, cutaneous glands (fig. 134), the secretion of which forms the cyst membrane. The oar-like tail may be long or short (stumpy-tailed cercaria) or entirely absent; its free end may be partly split (furcate cercaria), or split to its base (_bucephalus_); in various forms also the anterior end of the tail is hollow, and has enclosed within it the anterior body, which is otherwise free. The size also of the cercaria belonging to the different species is very diverse; in addition to forms swimming in the water that have the appearance of minute milky-white bodies, there are forms which measure as much as 6 mm. in length. [266] The cercaria is the characteristic larval stage of the Trematodes, and corresponds to a cysticercus or cysticercoid, though there is the important difference that the cercaria has an enteric cavity. According to some observers the enteron is represented by the frontal sucker of some Cestodes, and by the rostellum of the majority of others. The sporocyst and redia are regarded as intercalated stages, _viz._, as cercariæ exhibiting _pædogenesis_, _i.e._, development of young by a parthenogenetic process from individuals (_i.e._, cercariæ) not yet adult. The encysted cercariæ (fig. 135) are globular or oval, and are surrounded by a homogeneous membrane, which may be striated or contain granules. The tail is always cast off when encystment occurs, and organs peculiar to the cercaria stage (boring papilla, eyes) almost entirely disappear. On the other hand, the genitalia appear or become more or less highly developed, in extreme cases to such an extent that they become functional, and after autocopulation the creatures produce ova within the cysts. The cycle of development of the digenetic Trematodes has hitherto been generally explained as a typical ALTERNATION OF GENERATIONS, one sexual generation regularly alternating with one or two asexually reproducing generations. Recent authors, however, regard the cells in the sporocysts from which rediæ or eventually cercariæ arise as parthenogenetically developing ova, and the sporocysts as well as the rediæ as generations propagating parthenogenetically. In this case, however, it is an alternation of a sexual not with an asexual but with firstly a parthenogenetic generation (the sporocyst), the central cells of which are regarded as ova which develop parthenogenetically into the redia, and this the second parthenogenetic generation finally produces larvæ (cercariæ) capable of developing into the sexually mature form. Other authors, again, regard the development of the Digenea as only a complicated metamorphosis (p. 283), which is distributed over several generations before it is concluded. BIOLOGY. Endoparasitic Trematodes, as fully developed organisms, occur in vertebrate animals only, with very few exceptions; they inhabit almost all the organs (with the exception of the nervous and osseous systems and the male genitalia), but by preference the intestine in all its extent from the oral cavity to the anus; and, further, certain species or groups inhabit only quite restricted parts of the intestine. Besides in the intestine other species live in the liver, or in the bile-ducts, or in the gall-bladder; other accessory organs of the intestine, such as the pancreas, bursa Fabricii (of birds), are only infected by a few species. Many inhabit the lungs, or the air sacs in fowls, a few the trachea. Trematodes have also been known to occur in the urinary bladder, the urethra and the kidneys of all classes of vertebrates; they are also present in the vascular system of a few tortoises, birds and mammals; in birds they even penetrate from the cloaca into the oviducts, and are occasionally found enclosed in the laid eggs; one species is known to occur in the cavum tympani and in the Eustachian tube of a mammal (Dugong), another in the frontal sinus of the polecat; several species infest the conjunctival sac under the membrana nictitans of birds, one species even lives in cysts in the skin of song-birds. In an analogous manner the ectoparasitic Trematodes are not entirely confined to the surface of the body or the trachea of the lower vertebrate animals; a few species appear exclusively in the urinary bladder, in the œsophagus, and in the case of sharks in an accessory gland of the rectum. Trematodes live free and active within the organs attacked, though they may attach themselves by suction for a longer or shorter period; in other cases, however, they bore more or less deeply into the intestinal wall with their anterior end, or lie in cysts of the intestinal wall which only communicate with the lumen through a small opening; in those species living in the lungs of mammals the host likewise produces a cyst, which usually encloses two specimens; such association of a pair is also observed in other situations, and, though this is the rule in species sexually distinct, it is not entirely confined to these. As regards the AGE attained by endoparasitic Trematodes, there are but few reliable records, and these differ considerably; the overwhelming majority of species certainly live about a year, or perhaps a little longer, but there are some whose term of life extends to several or many years. Trematodes are but rarely found encysted in the higher vertebrate animals; the condition, however, is more frequent in amphibians, and especially in fishes, as well as in numerous invertebrate animals. CLASSIFICATION OF THE TREMATODES OF MAN. The following classification, partly artificial, partly natural, embraces only the flukes found in man:-- Order. *Digenea*, v. Beneden, 1858. Anterior sucker single and median, present. Eggs few. The (specialized) terminal portion of the uterus serves as a vagina. Development indirect, _i.e._, an intermediate host is required. Sub-order. *Prostomata*, Odhner, 1905. Mouth surrounded by the anterior sucker. Group. *Amphistomata*, Rudolphi, 1801, ep., Nitzsch, 1819. Gut forked, two suckers, the posterior sucker (acetabulum) terminal or ventro-terminal behind the genitalia, or at most embraced by the vitellaria. Skin with no spines. Excretory bladder a simple sac opening dorsally near hind end. Testes in front of ovary. Genital pore, median in anterior third of body. Thick flukes, almost circular in cross section. Family. *Paramphistomidæ*, Fischoeder, 1901. Amphistomata: Body not divided into a conical anterior portion and disc-like caudal portion. Ventral pouch absent. Sub-family. *Paramphistominæ*, Fisch., 1901. Paramphistomidæ: Oral sucker without evaginations. Not in man. Sub-family. *Cladorchiinæ*, Fisch., 1901. Paramphistomidæ: Oral sucker with evaginations; testes, two, deeply cleft (fig. 137). Genera: _Watsonius_, _Cladorchis_, etc. Family. *Gastrodisciidæ*, Stiles and Goldberger, 1910. Amphistomata: With body divided into a conical cephalic and disc-like caudal portion (fig. 138). Posterior sucker ventro-terminal. Oral sucker with evaginations. Genera: _Gastrodiscus_ and _Homalogaster_. Group. *Distomata*, Retzius, 1782. Gut forked, two suckers, the posterior sucker (acetabulum) ventral. It is always separated from the hind end by at least a part of the genitalia. Family. *Fasciolidæ*, Railliet, 1895. Large flat forms, genital pore _in front_ of ventral sucker, the latter powerful. Vitellariæ of numerous follicles, united by branching vitellarian ducts, at the sides of the body meeting posteriorly and extending ventrally and dorsally. Cirrus and vagina without spines. No crown of strong spines around sucker. Testes much branched. Uterus not well developed. Excretory bladder much branched. Eggs large. Sub-family. *Fasciolinæ*, Odhner, 1910. Large or median forms, gut much branched. Body has a shoulder separating head from body. Receptaculum seminis absent. Ovary branched, ventral sucker in anterior part of body. Genus: _Fasciola_. Sub-family. *Fasciolopsinæ*, Odhner, 1910. Shoulder absent. Receptaculum seminis present. Ovary branched, gut takes a zig-zag course with kinks on it, ventral sucker in anterior part of body. Genus: _Fasciolopsis_. Family. *Opisthorchiidæ*, Braun, 1901, emend. auctor. Ovary in front of testes. Small to medium flukes, very transparent, tapering anteriorly. Vitellaria moderately developed not extending in front of sucker. Cirrus absent. Seminal vesicle a twisted tube free in parenchyma. Testes near hind end one behind the other, lobed or branched, but not dendritically. Excretory bladder *Y*-shaped, the two limbs short, the stem *S*-shaped passing between the testes. Receptaculum seminis well developed. Laurer’s canal present. Uterine coils transverse, numerous. Eggs small. Sub-family. *Opisthorchiinæ*, Looss, 1899, emend. auctor. _Opisthorchiidæ_ in which the excretory pore is terminal. Excretory bladder long, dorsal to testes. Uterine coils not overlapping gut forks. Genera: _Opisthorchis_, _Paropisthorchis_, _Clonorchis_, _Amphimerus_, etc. Sub-family. *Metorchiinæ*, Lühe, 1909. _Opisthorchiidæ_ in which the excretory pore is ventral. Excretory bladder short, ventral to testes. Uterine coils partly overlapping gut forks and extend anteriorly beyond the sucker. Vitellaria compressed on the sides of the body. Genus: _Metorchis_. Family. *Dicrocœliidæ*, Odhner, 1910. Ovary _behind_ testes. Testes behind the ventral sucker, between it and the ovary. Body thin and transparent. Cirrus sac encloses the pars prostatica and seminal vesicle. Skin smooth. Gut forks do not reach posterior end. Receptaculum seminis and Laurer’s canal present. Vitellaria, moderate, lateral in mid-body slightly overlapping the gut. Uterus with an ascending and descending branch and numerous transverse coils extending to hind end. Eggs dark brown, 25 µ to 60 µ. Excretory bladder tubular in posterior third or half of body. Parasitic in bile-ducts of mammals and birds. Genus: _Dicrocœlium_. Family. *Heterophyiidæ*, Odhner, 1914. Ovary _in front_ of testes. Genital pore _behind_ or on a level with ventral sucker. Genital pore surrounded by a pseudo-sucker (_i.e._, its muscle is not sharply separated from but blends with the body muscles). Cirrus sac absent, consequently vesicula seminalis and pars prostatica lie free. Vagina and ejaculatory duct unite into a common duct before opening. Small and very small forms. Body covered with scales. Genera: _Heterophyes_, _Metagonimus_, etc. Family. *Troglotremidæ*, Odhner, 1914. More or less flattened Distomes of compact form, 2 to 13 mm. long. Ventral surface flat or somewhat hollowed, dorsal surface _arched_. Skin completely covered with pointed spines. Musculature weakly developed also in the suckers in those forms that inhabit cysts. Gut with pharynx and a not very long œsophagus and cæca, which end more or less shortly before the hind end. Excretory bladder *Y*-shaped or tubular. Pars prostatica and seminal vesicle always distinct. Testes elongated, symmetrically placed in or behind the middle of the body. Ovary directly in front of the testes, right-sided, generally much lobed. Receptaculum seminis and Laurer’s canal present. Vitellaria generally well developed, exclusively or for the most part confined to _the dorsal surface_, leaving only a median band unoccupied. Uterus either very long, coiling here and there, or shorter and more convoluted. Eggs in first case small 17 µ to 25 µ, in the second much larger 63 µ to 85 µ or even 120 µ (?) long. Parasitic in carnivora or birds, generally occurring in pairs in cyst-like cavities. Genera: _Paragonimus_, _Pholeter_, _Collyriclum_, _Troglotrema_. Family. *Echinostomidæ*, Looss, 1902. _More or less elongated flukes, small or very large, much flattened anteriorly, less so posteriorly, or even round. Suckers near one another, the anterior small and weak, the posterior large and powerful directed obliquely backwards. Surrounding the oral sucker dorsally and laterally but not ventrally is a fold or “collar” bearing a row or rows of pointed spines which are continued round laterally on to the ventral corners, the number being constant for each species, the corner spines large or specialized, skin anteriorly scaled or spiny. Alimentary canal consists of a pharynx, epithelial “pseudo-œsophagus” and gut cæca reaching to posterior end. Testes behind one another in hind body. Ovary on right side or median directly in front of the testes. Vitellaria lateral, usually extending to the hind end and not beyond the ventral sucker anteriorly. Genital pore just in front of ventral sucker. Uterus in transverse loops. Genital sinus absent or present. Receptaculum seminis and Laurer’s canal present. Eggs thin shelled and large, bright yellow, 65 µ to 120 µ long. Excretory bladder *Y*-shaped. Parasitic in gut of vertebrates, especially birds._ Sub-family. *Echinostominæ*, Looss, 1899. _Cirrus sac usually reaching to centre of ventral sucker, but not beyond. Cirrus long, usually without spines, coiled when retracted. Seminal vesicle tubular, twisted. On the head a ventral uniting ridge between the angles of the collar. Dorsal circlet of spines, single or double, not interrupted unless the collar itself is dorsally divided. Genera_: Echinostoma, etc. Sub-family. *Himasthlinæ*, Odhner, 1910. Cirrus sac reaching far beyond ventral sucker. Cirrus armed with strong rose-thorn-shaped hooks. Vesicula seminalis tubular not coiled. Cervical collar not continued across ventral aspect. Spines on collar in one row. Body armed with fine needle-shaped spines. Family. *Schistosomidæ*, Looss, 1899. Sexes separate. Genital pore behind the ventral sucker. Ventral sucker elevated above the surface. Pharynx absent. Gut forks reunite to form a single stem. In ♂ four or more testicular follicles. In ♀ a single ovary, just in front of the union of the gut forks. Vitellaria on either side of the united gut stem. THE TREMATODES OBSERVED IN MAN. Family. *Paramphistomidæ*, Stiles and Goldberger, emend. 1910. Sub-family. *Cladorchiinæ*, Fisch., 1901. Genus. *Watsonius*, Stiles and Goldberger, 1910. _Cladorchinæ_.--Body pyriform. Ventral pouch absent. Acetabulum ventral or (?) ventro-subterminal, very large, margins projecting, aperture small. Genital pore in front of bifurcation of gut, not surrounded by a sucker; ductus hermaphroditicus apparently absent. Excretory pore at posterior end of excretory vesicle, behind Laurer’s canal. Oral sucker with a pair of irregularly globular suctorial pouches; œsophagus thickened distally; cæca long, not wavy; end in acetabular region. _Male Organs_.--Testes two lobed, smaller than acetabulum; longitudinally, nearly or quite coinciding; transversely they abut or slightly overlap; preovarial in equatorial and caudal thirds. Pars musculosa not largely developed; cirrus pouch absent. _Female Organs_.--Ovary and shell gland post-testicular. Vitellaria extend from gut fork to slightly beyond gut ending; uterus intercæcal, partly post-testicular. Laurer’s canal in front of excretory vesicle. _Type Species_.--_Watsonius watsoni_, Conyngham, 1904. *Watsonius watsoni*, Stiles and Goldberger, 1910. Syn.: _Amphistomum watsoni_, Conyngham, 1904; _Cladorchis watsoni_, Shipley, 1905. _Body_, 8 to 10 mm. long, by 4 to 5 mm. broad, by 4 mm. thick; tapers anteriorly to 2·5 mm. Caudal extremity bluntly rounded, venter surrounded by an elevated ridge, surface with transverse ridges best defined ventrally. Genital pore median about one-quarter of body length from anterior end at level of suctorial pouches. Acetabulum 1 mm. in diameter, margin projecting, aperture small. Mouth in a groove with digitate papillæ. Oral sucker very large, one-fifth of length of body, with a pair of irregularly globular pouches. Œsophagus somewhat longer than sucker. Excretory pore at the level of the acetabular aperture. The vesicle extends from the plane of the transverse vitelline ducts to centre of acetabulum. [Illustration: FIG. 136.--_Watsonius watsoni_: ventral view. 4/1. (After Shipley.)] _Male Organs_.--Testes deeply notched adjoining one another. Vesicula seminalis much coiled and dilated, pars musculosa not coiled. Pars prostatica (?) dilated, ejaculatory duct long and narrow, opening on a papilla; genital atrium papillated. _Female Organs._--Ovary dorso-posterior of posterior testis. Shell gland dorsal to ovary. Vitellaria ventral and lateral to gut cæca extending from gut fork to equator of acetabulum. Uterus dorsal to testes, ductus hermaphroditicus absent. Laurer’s canal opens in dorso-median line slightly behind anterior border of sucker. [Illustration: FIG. 137.--_Watsonius watsoni_: ventral projection composed from a series of transverse sections. _o.s._, oral sucker; _s.p._, suctorial pouch; _ga._, genital atrium; _d.e._, ejaculatory duct; _es._, œsophagus; _e.g._, œsophageal ganglion; _p.p._, pars prostatica; _p.m._, pars musculosa; _i._, gut; _ut._, uterus; _v.e._, vas efferens; _v.e.s._, left vas efferens; _v.e.d._, right vas efferens; _v.g._, vitellarium; _t._, testes; _ov._, ovary; _s.g._, shell gland; _t.vd._, transverse vitelline duct. (After Stiles and Goldberger.)] _Eggs._--123 µ to 133 µ long by 75 µ to 80 µ broad. _Habitat._--Jejunum and duodenum of man, German West Africa. The parasite has only been found once in man. The patient, a negro from German West Africa, died at Zola, Northern Nigeria. The symptoms were persistent watery diarrhœa without blood or mucus. The parasites were also passed in the stools. It occurs also in monkeys. Family. *Gastrodisciidæ*. Genus. *Gastrodiscus*, Lkt., 1877. Acetabulum small, caudal and ventral margin raised, aperture relatively large. Genital pore without sucker. Excretory pore post-vesicular, posterior to opening of Laurer’s canal. Œsophagus with muscular thickening; cæca not wavy, long, end post-equatorial and post-testicular. _Male Genitalia._--Testes two, branched pre-ovarial. _Female genitalia._--Ovary and shell gland post-testicular. Vitellaria extracæcal; uterus intercæcal; Laurer’s canal entirely prevesicular. _Type._--_Gastrodiscus ægyptiacus_, Cobbold, 1876. *Gastrodiscus hominis*, Lewis and McConnell, 1876.[267] Syn.: _Amphistomum hominis_, Lew. and McConn. [267] Leiper places this species in a new genus _Gastrodiscoides_. Genus _Gastrodiscoides_, Leiper, 1913, distinguished from _Gastrodiscus_ by: (1) large genital cone; (2) position of genital orifice; (3) disc without papillæ; (4) testes one behind the other. [Illustration: FIG. 138.--_Gastrodiscus hominis._ Slightly magnified. (After Lerckart.)] _Body_, reddish in the fresh, 5 to 8 mm. long; posteriorly, 3 to 4 mm. broad. The disc has incurved edges which are interrupted in front where it joins the anterior cylindrical portion and posteriorly behind the ventral sucker. The disc itself and ventral surface are covered with a number of (microscopic) papillæ. Pharynx provided with two diverticula or pouches. The bifurcation of the gut lies sometimes above, sometimes below the level of the genital pore. The gut cæca end about the level of the centre of the acetabulum. _Genital Pore._--About the middle of the conical anterior portion. (It appears to be surrounded by a muscular sucker.) Leiper (1913) describes the ducts as discharging at the tip of a large fleshy papilla, the surface of which bears cuticular bosses. _Testes_ much lobed, the anterior is smaller than the posterior and lies at about the level where the anterior conical portion joins the disc. The posterior testis just in front of the anterior margin of the acetabulum separated from it by the ovary. The ovary, somewhat oval in shape or slightly constricted in the middle, lies slightly to the right of the median line. Dorsal to it lies the well-developed shell gland, Laurer’s canal opening in front of the excretory bladder. The excretory bladder is a long sac with its opening at its posterior extremity about the level of the middle of the acetabulum. The vitellaria are restricted in extent. They do not extend forward beyond the anterior border of the posterior testis. They are best developed in the area between the acetabulum and the termination of the gut cæca. The eggs are oval and measure 150 µ in length by 72 µ in breadth. _Habitat._--Cæcum and large intestine of man. Also in the pig (5 per cent.) in Annam. _Distribution._--This parasite has been recorded from Assam (not uncommon), British Guiana (Indian immigrants), and Cochin China. _Gastrodiscus ægyptiacus_, Cobbold, 1876, and _G. secundus_, Looss, 1907, occur in the horse; _G. minor_, Leiper, 1913, in the pig in Nigeria and Uganda. Family. *Fasciolidæ*, Raill., 1895. Sub-family. *Fasciolinæ*, Odhner, 1910. Genus. *Fasciola*, L., 1758. The ventral sucker is situated at the level of the junction of the cone with the body, _viz._, at the level of the “shoulder,” and is large and powerful. The cuticle is covered with strong spines; the gut cæca run in the mid-line to the hind end, and are provided with numerous long lateral and fewer and shorter median branches. The ovary lies on one side in front of the transverse vitelline duct; the testes lie obliquely one behind the other. The uterus, in the shape of a rosette, lies in front of the genitalia. Laurer’s canal is present; the vesicula seminalis lies in the cirrus pouch; the ova are large, not very numerous, and only develop after they have been deposited. Parasites of the biliary ducts of herbivorous animals. *Fasciola hepatica*, L., 1758. Syn.: _Distomum hepaticum_, Retz., 1786; _Fasciola Humana_, Gmel., 1789; _Distomum caviæ_, Sons., 1890; _Cladocœlium hepaticum_, Stoss., 1892. Length 20 to 30 mm., breadth 8 to 13 mm., cephalic cone 4 to 5 mm. in length and sharply differentiated from the body by a shoulder on each side. Spines in alternating transverse rows and extending on the ventral surface to the posterior border of the testes, and on the dorsal surface not quite so far. The spines are smaller on the cephalic cone than on the posterior part of the body, where they are discernible with the naked eye. The suckers are hemispherical, and near each other; the oral sucker is about 1 mm. and the ventral sucker about 1·6 mm. in diameter. The pharynx, which includes almost the entire œsophagus, measures 0·7 mm. in length and 0·4 mm. in breadth. The intestine bifurcates at the limit of the cephalic cone and the branches are even here furnished with diverticula directed outwardly. The ovary is ramified and situated in front of the transverse vitelline duct, usually on the right side; the shell gland lies near the ovary in the median line; posterior to the transverse vitelline ducts are the greatly ramified testes, which occupy the greater portion of the posterior part of the body, with the exception of the lateral and posterior border; the long vasa efferentia only unite as they enter the cirrus pouch. The vitellaria occupy the sides of the posterior part of the body, commencing at the level of the ventral sucker and uniting behind the testes. The ova are yellowish-brown, oval, operculated, 130 µ to 145 µ in length, 70 µ to 90 µ in breadth (average size 132 µ by 70 µ). [Illustration: FIG. 139.--_Fasciola hepatica_, L. From a specimen that is not yet mature, showing the gut and its branches. 5/1.] The Liver Fluke inhabits the bile-ducts of numerous herbivorous mammals (sheep, ox, goat, horse, ass, rabbit,[268] guinea-pig, squirrel, beaver, deer, roe, antelope, camel, kangaroo, and others), and is distributed over the whole of Europe, though not to an equal extent. It is further known in North Africa, in North and South America, as well as in Australia; it is also found in Asia, as it has been reported from Japan, China, and Tonkin (Gaide, two cases in man). In some districts of Germany it is very frequent, and the slaughter-house statistics of various places show that it is of daily occurrence. _Fasciola magna_ occurs in herbivora in America. [268] [There does not seem to be any direct evidence of either rabbits or hares normally being invaded by this fluke.--F. V. T.] The liver fluke, however, is by no means a harmless parasite, for it produces in domestic animals, more especially in sheep, a disease of the liver that appears epidemically in certain years and districts, and commits great ravages amongst the flocks. [The following records show the enormous loss caused in sheep by this parasite. In 1812, in the Midi, principally in the Departments of the Rhône, Herault, and Gard, the disease was rampant; 300,000 sheep perished in the Arles territory, and 90,000 in the Arrondissements of Nîmes and Montpellier. In 1829 and 1830, in the Department of the Meuse and near localities, not only sheep but oxen died in enormous numbers; for instance, in the Arrondissement of Verdun out of 50,000 sheep 20,000 died, and out of 20,000 cattle 2,200 died. In England, in 1830, 2,000,000 sheep were carried off; whilst in 1862 60 per cent. of the sheep died in Ireland; and in 1879 over 300,000 were lost in England; whilst as late as 1891 one owner in the same country lost over 10,000 sheep (_Live Stock Journal_, October 30, 1891).--F. V. T.] [Illustration: FIG. 140.--_Fasciola hepatica._ _M._, mouth; _Ut._, uterine rosette; _Tr.c._, transverse vitelline ducts uniting to form a vitelline receptacle in the mid-line; _E.d._, longitudinal vitelline ducts; _V.s._, vitellaria. The clear space in the centre represents the position of the ramifying testes and part of the gut. Natural size. (Mull. fluid, alcohol, creosote, Canada balsam.)] [Illustration: FIG. 141.--_Fasciola hepatica_, L. _I._, intestine; _Vs._, vitellaria; _Ov._, ovary; _O._, oral aperture; _Ut._, uterus; _S._, ventral sucker; _T._, testes. In front of the testes are seen the transverse vitelline ducts uniting to form the pyriform vitelline receptacle. Immediately in front of this the spherical shell gland. The two vasa efferentia can also be seen running up in the mid-line. The branches of the gut are only shown in the cephalic cone. (After Claus.)] The disease usually commences towards the end of summer with an enlargement of the liver, induced by the invasion of numerous young flukes; in the autumn and winter the animals suffer from the consequences of disordered biliary secretion; they become feverish, emaciated, and anæmic, and lose their appetite. In consequence of the consecutive atrophy of the liver, œdema and ascites set in, and many animals succumb to this “liver rot.” On examination the liver is found to be shrunken, the bile-ducts are enormously dilated and in parts saccular and full of flukes. Should the animals survive this stage, spontaneous recovery ensues in consequence of the flukes commencing to leave the liver in the spring, but the liver remains changed and its sale is prohibited[269] when the changes are extensive.[270] [269] [This is not the case in Great Britain; fluky sheep are sent to market, there being no danger to man from eating the flesh.--F. V. T.] [270] As an example, this occurred in Berlin in the case of 19,034 oxen, 15,542 sheep, 1,704 pigs, and 160 calves in the period of 1883–1893; during which time 719,157 oxen, 1,519,003 sheep, 2,258,110 pigs, and 567,964 calves were slaughtered. As a matter of fact, however, the number of infected beasts was really larger. [The following stages may be noticed in sheep suffering from fascioliasis. Gerlach recognized four stages, based on the varied relations that the flukes contract with the liver of their host. These periods are sometimes very marked, but at others, owing to subsequent infections, the features become merged and so obliterated. But when a single infestation occurs they are very marked. [The first period is called the PERIOD OF IMMIGRATION. This occurs at the fall of the year and generally passes unperceived, as the young flukes do little harm to the liver. It varies from four to thirteen weeks. Gerlach has remarked upon cases of death from apoplexy at this period. [The second period is the PERIOD OF ANÆMIA. This occurs in November and December. The sheep at first fatten rapidly, but later the mucous membranes become pale and of a yellowish hue, and the sheep become sluggish and cease to feed. The fæces are normal, but may contain fluke ova. [Illustration: FIG. 142.--_Fasciola hepatica_: egg from liver of sheep. _o_, operculum, _e_, segmenting ovum. The rest of the space is occupied by yolk cells, the granules in three only being shown. × 680. (After Thomas.)] [Illustration: FIG. 143.--_Limnæus truncatulus_, Müll., the intermediate host of _Fasciola hepatica_. _a._, natural size; _b._, magnified. (From Leuckart.)] [The third period is the PERIOD OF WASTING. This corresponds with the beginning of January--about three months after the entry of the larvæ. Emaciation now becomes very marked, the skin and mucous membranes blanched, temperature variable and marked by an irregular curve; respiration laboured and quick; appetite regular; abortion frequently occurs in pregnant ewes; pressure on the back causes the animals to fall; local œdemas occur, the most perceptible in the submaxillary space, extending below the larynx and over the cheeks and parotids (called “bourse,” “boule” in France; “watery poke” or “cockered” in England). Death usually occurs at this period, but a fourth stage may occur. [The fourth period is the PERIOD OF MIGRATION OF THE FLUKES. This is a period of convalescence and recovery, generally in May and June.--F. V. T.] Oxen suffer less in general, but even in these animals “stray” hepatic flukes are occasionally found in the lungs, enclosed in thick-walled cysts. _Pathological Anatomy._--The bile-ducts are conspicuous on the surface of the liver. They are thickened and much dilated and in parts saccular, and considerable atrophy of the liver cells accompanies the condition. Histologically there is immense proliferation of the epithelium of the bile-ducts leading to “adenomata.” The LIFE-HISTORY of the liver fluke was discovered by R. Leuckart and P. Thomas. According to these investigators the elongated miracidium (fig. 131, _a_) ciliated all over develops from the eggs a few weeks after the latter (fig. 142) have reached the water, and after it has become free the embryo penetrates and becomes a sporocyst (fig. 131, _b_) in a water-snail (_Limnæus truncatulus_, Müll. = _L. minutus_, Drap.) that is common in fresh water, and can live in the smallest collection of water as well as in fields that have been flooded. The sporocyst first of all produces rediæ, which remain in the same host (and under certain circumstances, _e.g._ in summer, these develop a second generation of rediæ), and these finally form cercariæ (fig. 134). The latter become encysted on blades of grass and are taken up by the respective hosts with their food; this takes place towards the end of summer, while the sheep feeding on the pasture land in the spring spread the eggs of the fluke, and sometimes the fluke itself, by passing them with their fæces. In districts where _Limnæus truncatulus_ is absent, analogous species act as the intermediary hosts, of which one example according to Lutz is _Limnæus oahuensis_ in the Sandwich Islands. [The host in Europe is _Limnæus truncatulus_. This snail extends from Siberia to Sicily and Algeria, and according to Captain Hutton is a native of Afghanistan. It also occurs in Thibet, Amoor, Morocco, Tunis, Canary Islands and the Faroe Islands. It deposits its eggs or spawn upon the mud around ponds, ditches and streams. The eggs are laid in batches of thirty to a hundred, each snail laying as many as 1,500 eggs; they are united into strips of a gelatinous substance. In about two weeks young snails appear. It is amphibious, being more frequently met with out of the water than in it. It occurs in elevated spots as well as in low-lying districts. Moquin-Tandon found it at 4,000 feet in the Pyrenees. In the allied species, _L. peregra_, the fluke will develop up to a certain stage, but never completes all its varied phases. [In South America the host is probably _Limnæus viator_, Orb., and in North America _Limnæus humilis_, Say.--F. V. T.] In human beings as well as in some of the mammals quoted above, the liver fluke is only a casual parasite, and hitherto only twenty-eight cases have been observed in man; the infection was mostly a mild one and there were no symptoms, or only very trifling ones; a few isolated cases were only discovered _post mortem_. Occasionally, however, even when the infection was inconsiderable, severe symptoms were set up, which in isolated cases led to death. The symptoms (enlargement and painfulness of the liver, icterus) merely pointed to a disease of the liver. _Diagnosis_ can only be established by finding eggs in the fæces. Care should be taken not to confuse them with those of _Dibothriocephalus latus_. HALZOUN. [Illustration: FIG. 144.--Young _Fasciola hepatica_, soon after entry into the liver. The intestinal cæca have lateral diverticula. Magnified. (From Leuckart.)] In North Lebanon, the liver fluke is, according to A. Khouri, a frequent parasite of man, not in the liver, however, but in the pharynx. The occurrence in this unusual site is effected by the eating of raw infected livers, especially those of goats (_Capra hircus_). The flukes thus taken in do not all reach the stomach, where they would be soon killed, but some of them attach themselves to the pharyngeal mucosa and to the adjoining parts, and there cause inflammation and swelling, which lead to dyspnœa, dysphagia, dysphonia and congestion of the head, sometimes even to still more severe symptoms, and even death. The affection termed “Halzoun” lasts some hours or several days, and after vomiting recovery sets in. In other cases man becomes infected in the usual way by ingesting cysts attached to grass or the underside of leaves of plants (_e.g._, Rumex sp.), where they are overlooked from their scanty size (0·2 to 0·3 mm.). [Illustration: FIG. 145.--_Fasciola gigantica._ × 6-1/2 (After Looss.)] As the liver fluke feeds on blood it is possible that it also reaches, particularly when young, the circulatory system, and cases have been known in which it has been carried by the blood into organs far from its original situation. Such cases also have been repeatedly observed in men. Probably the parasite described by Treutler, 1793, as _Hexathyridium venarum_, which protruded from the ruptured anterior tibial vein of a man, was a young liver fluke. A few adult specimens were found by Duval in the portal and other veins _post mortem_ at Rennes (1842) in a man, aged 49, and a similar statement is reported by Vital from Constantine (1874). Giesker, in 1850, found two hepatic flukes in a swelling on the sole of the foot of a woman. Penn Harris states that he observed six specimens in Liverpool in a spontaneously ruptured abscess of the occiput of a two months old infant. Another case which, like the previous one, is reported by Lankester,[271] relates to a sailor who suffered from an abscess behind the ear, and from which a liver fluke was expelled. Finally, Dionis de Carrières reports the case of a man, aged 35, in whose right hypochondriac region a tumour the size of a pigeon’s egg had formed, and from which a young liver fluke was extracted. [271] In the English translation of Küchenmeister’s work on Parasitology (London, 1857). The specimen is preserved in the Hunterian Museum, London, and is an adult liver fluke, measuring 18 mm. in length and 7 mm. in breadth. From such records it is not impossible that _Distomum oculi humani_, Ammon, 1833, as well as _Monostomum lentis_, v. Nordm., 1832, may have been very young hepatic flukes that had strayed. Ammon found four specimens (length 0·5 to 1 mm.) of his species (named _Distomum ophthalmobium_ by Diesing in 1850) between the opaque lens and the capsule of a five months old child in Dresden, and von Nordmann discovered his _Monostomum lentis_ to the number of eight specimens (only 0·3 mm. in length) in the opaque lens of an old woman. Minute white bodies which Greef found in the cortex of the lens of a fisherman, aged 55, removed on account of cataract, were with some reserve regarded as Trematode larvæ. The fact that Ammon found that the intestinal cæca of the worm discovered by him had no lateral branches does not negative the above opinion, as in the liver fluke the intestinal cæca are originally unbranched, and according to Lutz they only develop lateral ramifications later, between the twelfth and twenty-second day of infection (fig. 144). *Fasciola gigantica*, Cobbold, 1856. Syn.: _Distomum giganteum_, Diesing, 1858; _Fasciola gigantea_, Cobbold, 1858; _Cladocœlium giganteum_, Stoss., 1892; _Fasciola hepatica_ var. _angusta_, Raill., 1895; _Fasciola hepatica_ var. _ægyptiaca_, Looss, 1896. This species is closely allied to _Fasciola hepatica_, but is distinguished by its elongated body, short cephalic cone, almost parallel sides, larger ventral sucker, which is also closer to the oral sucker, and by its larger eggs. Length up to 75 mm., width up to 12 mm. Oral sucker 1 to 1·2 mm., ventral sucker up to 1·7 mm. in diameter. Eggs 150 µ to 190 µ long by 75 µ to 90 µ broad. _Habitat._--Bile-ducts of _Camelopardalis giraffa_, _Bos taurus_, _Bos indicus_, _Bos bubalis_, _Ovis aries_ and _Capra hircus_. _Distribution._--Africa. This species has once been observed in man by Gouvea, in Rio de Janeiro, in a French naval officer who became ill with fever, cough and slight blood-spitting. The lungs were normal except for a sharply circumscribed spot at the base of the left lung. Twenty days later during a fit of coughing the patient spat up a fluke 25 mm. long, characterized by its slender aspect and by the size of its ventral sucker, and its close proximity to the oral sucker. Considering the fact that Gouvea’s patient had spent many weeks in July of the same year in Dakar (Senegambia), where according to Railliet _Fasciola gigantica_ is common in slaughtered animals, and considering also the characters of the fluke, Railliet rightly assumes that one had to do with the African giant fluke and that the patient had infected himself in Dakar. Sub-family. *Fasciolopsinæ*, Odhner, 1910. Genus. *Fasciolopsis*, Looss, 1898. Ventral sucker large, and elongated posteriorly into a sac. Cirrus pouch long and cylindrical, its greatest length being occupied by the sinuous tubular seminal vesicle, on which exists a peculiar cæcal appendage. Laurer’s canal present. *Fasciolopsis buski*, Lank., 1857. Syn.: _Distomum buski_, Lank., 1857; _Dist. crassum_, Cobbold, 1860, _nec_ v. Sieb., 1836. [Illustration: FIG. 146.--_Fasciolopsis buski_, Lank. _V.s._, ventral sucker; _C.p._, cirrus pouch; _I._, intestinal fork; _S.v._, vitellaria; _T._, testes; _O._, ovary; _Ms._, sucker; _Shg._, shell gland; _Ut._, uterus. Magnified. (After Odhner.)] The length of the body varies; it may measure 24 to 37 or even attain 70 mm.; the breadth is from 5·5 to 12 to 14 mm. In the pig the fresh parasites measure, smallest, 12 to 8 mm.; largest, 35 to 16 mm. (Mathis and Léger). Skin without spines, but according to Heanly always present in man and pig specimens. The oral sucker measures 0·5 mm. in diameter; the ventral sucker is three to four times as large; the pharynx is globular, 0·7 mm. in diameter; the prepharynx is provided with a sphincter; the intestinal cæca extend to the posterior border with two characteristic curves, one at the anterior border of the anterior testis, the other between the two testes. The genital pore is at the anterior border of the ventral sucker; the cylindrical cirrus pouch extends from behind the ventral sucker to half-way to the shell gland. The seminal vesicle extends forwards within the cirrus pouch as a convoluted tube. From its anterior portion is given off the cæcal appendage, which has itself short lateral diverticula. It runs backwards, ending blindly about 0·5 mm. from the posterior end of the cirrus sac. The seminal vesicle is continued as the pars prostatica (?) 0·5 mm. long, and this by the very short ejaculatory duct (13 µ), and finally by the fairly long cirrus, which is beset with very fine spines except at either extremity. The ovary and shell gland are situated at about the middle of the body with the testes behind them, and the uterus in front. The vitellaria extend from the ventral sucker to the posterior border. The eggs measure 120 µ to 130 µ in length and 77 µ to 80 µ in breadth, and resemble those of Echinochasma sp. in dogs. The larval stages are said to occur in shrimps. _Habitat._--Intestine of pig and man. _Distribution._--In man: India, Siam, China, Assam, Sumatra. It is common in Cochin China (16 out of 133 Annamites, Noc.), in Tonkin very rare. Dr. J. Bell has sent me [J. W. W. S.] human specimens from Hong Kong. In pigs: very common in South China (Heanly). Common in pigs in Hong Kong. Sixteen out of 248 pigs (_i.e._, 6 per cent.) infected in Hanoi. *Fasciolopsis rathouisi*, Ward, 1903. Syn.: _Distomum rathouisi_, Poirier, 1887. [Illustration: FIG. 147.--_Fasciolopsis rathouisi_, Poir.: the mouth at the top, and under it the genital pore and ventral sucker, behind which again is the uterus. The vitellaria are at the sides, and posteriorly in the central field the ramified testes; the ovary is in front of the right testis. (After Claus.)] Fifteen to 19 mm. long by 8·5 to 10·5 mm. broad by about 3 mm. thick. Skin with spines (Leiper). Bluntly oval or elliptical with short cephalic cone which is absent in _Fasciolopsis buski_. Oral sucker subterminal, 0·25 to 0·29 mm. broad by 0·2 mm. in antero-posterior diameter. Distant from ventral sucker by about twice its diameter. Ventral sucker 1·32 to 1·38 mm. broad by 0·68 to 0·7 mm. in antero-posterior diameter. Œsophagus extremely short. Cirrus sac not conspicuous and straight as in _Fasciolopsis buski_, but is convoluted. Testes one behind the other (according to Poirier they lie beside one another), more compactly branched, broader and denser than in _Fasciolopsis buski_. Ovary on right side, small, coarsely branched. Uterus in broad, closely grouped coils, packed with ova anterior to ovary. Vitellarian acini more numerous and somewhat differently distributed. Eggs 150 µ by 80 µ, thin shelled. [H. B. Ward, who has examined this species, and from whose account the above is mainly taken, considers that it is a good species, although the differences between it and _Fasciolopsis buski_ are slight, while Odhner, who examined the original species, is of the opposite opinion.--J. W. W. S.] The parasite appears to cause diarrhœa, wasting and occasionally jaundice. _Habitat._--Intestine of man. _Distribution._--China, common in some parts (Goddard). *Fasciolopsis goddardi*, Ward, 1910. Twenty-one to 22 mm. long, 9 mm. broad. Skin with spines (Leiper). Uterus very closely coiled, most striking character is the large size of the vitelline acini. Imperfectly known. _Distribution._--China (Shanghai). *Fasciolopsis fülleborni*, Rodenwaldt, 1909. The fully extended fluke is tongue-shaped, 50 by 14 mm.; two contracted specimens measured 40 by 15 mm. and 30 by 16 mm. respectively. Skin without spines, with according to Leiper cephalic cone not clearly defined. Oral sucker circular, 0·75 mm. in diameter, slightly larger than that of _Fasciolopsis buski_. Ventral sucker 2·6 mm. in diameter (that of _Fasciolopsis buski_ 1·6 to 2 mm.). Length 2·9 mm. (as in _Fasciolopsis rathouisi_), the excess of length over breadth being due to the posterior elongated sac-like prolongation of the sucker. Prepharyngeal sphincter present. Pharynx 0·7 mm. in diameter. Œsophagus practically absent. Gut cæca similar to those of _Fasciolopsis buski_. _Testes_--regularly branched, separated by an incurving of the cæca, the anterior occupying a smaller area than the posterior. _Ovary_--very small, as in _Fasciolopsis buski_, on the right side. _Shell Gland_--almond-shaped, 2·3 by 1·2 mm. In _Fasciolopsis buski_ it is round and smaller, 1 to 1·5 mm. in diameter. _Vitellaria_--similar in distribution to those of _Fasciolopsis buski_, but the acini are strikingly small. [Illustration: FIG. 148.--_Fasciolopsis fülleborni_, ventral aspect. (After Fülleborn.)] _Cirrus Sac_--is the most characteristic feature of this species. It is a powerfully built, convoluted sac standing out clearly on the body. It is not a uniform, straight cylinder 0·25 to 0·33 mm. in diameter, as in _Fasciolopsis buski_, but even in fully extended flukes is typically convoluted. It is 1 mm. thick in the middle, but in other parts varies much from this. The posterior end of the cirrus sac is at two-thirds or more of the distance from ventral sucker to shell gland. In the case of _Fasciolopsis buski_ the posterior end of the sac only extends half-way. _Seminal Vesicle_--has a peculiar convoluted, saccular and angular course, but the cæcal appendage characteristic of the genus appears to be absent! _Excretory System._--The main stem gives off very regular transverse branches which are well seen posteriorly. _Eggs._--100 µ by 73 µ. Thin shelled. _Habitat._--Intestine. Mahommedan from Calcutta. [It is evident that a re-examination of fresh material is required before the validity of all these species can be accepted.--J. W. W. S.] Family. *Troglotremidæ*, Odhner, 1914. Genus. *Paragonimus*, Braun, 1899. Body egg-shaped or somewhat elongated, generally more broadly rounded in front than behind. Covered all over with spear-shaped spines _arranged in groups_. Gut cæca winding with dilatations or constrictions in parts. Ventral sucker in or in front of the middle of the body. Excretory bladder cylindrical, very long and broad, reaching in front to the bifurcation of the gut. The lateral excretory canals join the bladder only a little in front of the excretory pore. Genital pore median just behind the ventral sucker. Genital sinus duct-like. Cirrus sac absent. Male terminal organs very small. Ejaculatory duct present. Testes and ovary deeply lobed, the testes in or just behind the middle, the ovary somewhat laterally placed just _behind_ the ventral sucker. Uterus forms a coil behind the ventral sucker. Eggs rather large, thin shelled, the ovarian cell still unsegmented on deposition. Receptaculum seminis, small. Parasitic in the lungs of mammals, enclosed in cyst-like cavities, generally in pairs. _Type Species._--_P. westermanii_ in the tiger. *Paragonimus ringeri*, Cobb., 1880. Syn.: _Distoma ringeri_, Cobb., 1880; _Distoma pulmonale_, Baelz, 1883; _Distoma pulmonis_, Suga, 1883. The body is of a faint reddish-brown colour and plump oval shape. The ventral surface a little flattened; 7·5 to 12 mm. in length, 4 to 6 mm. in breadth, and 3·5 to 5 mm. thick (in man). The oral sucker (0·75 mm.) is subterminal; the ventral sucker (0·8 mm.) somewhat in front of the middle of the body. Pharynx spherical, 0·3 mm. in diameter, or 0·4 by 0·3 mm.; œsophagus, 0·02 mm.; intestinal cæca convoluted, asymmetrical, the first part having the same structure as the œsophagus. The cuticle is covered with spines in groups; the excretory pore opens at the posterior end rather on the ventral surface, the excretory ducts open into the elongated bladder at the hind end near the pore. Genital pore behind the ventral sucker and median. Genital sinus 0·2 mm. long with thick wall, ejaculatory duct 0·13 mm., pars prostatica 0·2 mm., seminal vesicle duct-like of irregular outline. Behind the sucker the ovary on the left, and the closely packed uterine coil on the right (though amphitypy of these two organs is common); the two irregularly lobed testes lie side by side posteriorly. Vitellaria extensive, leaving only a median dorsal and ventral space free. Seminal receptacle probably absent; Laurer’s canal present. The eggs are oval, brownish-yellow, fairly thin shelled, and measure on an average 81·2 µ by 49·2 µ. [Illustration: FIG. 149.--_Paragonimus ringeri_, Cobb.: to the right, dorsal aspect; to the left, ventral aspect. Natural size. (After Katsurada.)] [Illustration: FIG. 150.--_Paragonimus ringeri_, Cobb.: diagram of the internal organs. _a_, œsophagus; _b_, vitellaria (a portion only shown); _c_, common genital duct; _d_, shell gland with oviduct, Laurer’s canal and vitelline duct; _e_, ovary; _f_, vitelline receptacle; _g_, excretory pore; _h_, oral sucker; _i_, pharynx; _k_, gut; _l_, ventral sucker; _m_, uterine coils; _n_, vitellarian ducts; _o_, vas efferens; _p_, testis. (After Kubo.)] [Illustration: FIG. 150A.--_Paragonimus westermanii_, Kerb.: seen from the ventral surface. Mouth, pharynx, intestinal cæca, at the sides of which the vitellaria are observed. The genital pore is behind the ventral sucker, and next to it, on the left, the ovary; on the right, the uterus; the two testes posteriorly; the excretory vessel in the middle, 10/1. (After Leuckart.)] The following species are also known:--_P. westermanii_, Kerb., 1878, in the tiger, and _P. kellicotti_, Ward, 1908, in the pig, dog, and cat (N. America). Ward and Hirsch give the following differences between the spines of the three forms:-- _P. ringeri._ _P. westermanii._ _P. kellicotti._ Shape Chisel-shaped, Lancet-shaped, Chisel-shaped, moderately heavy. very slender. heavy. Distribution Circular rows, in Circular rows, Circular rows, groups. in groups. singly. Two other species, _P. rudis_, Diesing, 1850, in a Brazilian otter (_Lutra brasiliensis_) and _P. compactus_, Cobbold, 1859, in the Indian ichneumon, are but little known. _Habitat._--Lungs, pleuræ, and especially the bronchi of man and dog. The alleged occurrence (of eggs) in other organs may be due to confusion with those of _Schistosoma japonicum_. _Distribution._--China, Korea, and especially in Japan, where, according to Katsurada, there are no districts that are entirely free from pulmonary flukes. The _mountainous_ provinces of Okayama, Kumamoto, Nagano and Tokushima are the principal centres. [Illustration: FIG. 151.--Egg of _Paragonimus ringeri_, Cobb., from the sputum. Showing the ovarian cell and vitelline cells and granules. 1,000/1. (After Katsurada.)] _Pathology._--The number present in the lung varies from two to twenty, about. Usually one cyst contains one worm, but in the dog each cyst contains two. The cysts admit the tip of the finger, and have a fibrous wall 1 mm. thick. They originate partly from dilatation of bronchi and bronchioles. Others arise from the inflammatory reaction of lung tissue into which the worms have wandered. The worms and their eggs cause bronchitis and peribronchitis, catarrhal, hæmorrhagic, or purulent, and areas of consolidation. Areas containing eggs in their centre resembling tubercle nodules are not uncommon, and extensive cirrhosis of the lung may be found. As a result of these changes, emphysema and bronchiectasis also occur. As to the development, only the following details are known: that the eggs, which before segmentation of the ovum reach the open in the sputum and through being swallowed also in the fæces, develop in water into a miracidium ciliated all over, which hatches and swims about freely. According to Manson this takes place in four to six weeks. Sub-family. *Opisthorchiinæ*, Looss, 1899. Genus. *Opisthorchis*, R. Blanch., 1845. Opisthorchiinæ with lobed testes. Laurer’s canal present. Parasitic in the bile-ducts of mammals and birds. *Opisthorchis felineus*, Riv., 1885. Syn.: _Distoma conus_, Gurlt, 1831 (_nec_ Creplin, 1825); _Distoma lanceolatum_, v. Sieb., 1836, v. Tright, 1889 (_nec_ Mehlis, 1825 = _Fasciolo lanceolata_, Rud., 1803); _Distoma sibiricum_, Winogr., 1892; _Distoma tenuicolle_, Mühl., 1896. This parasite is yellowish-red in the fresh condition, and almost transparent. The body is flat, with a conical neck at the level of the ventral sucker marked by a shallow constriction; this, however, is only noticeable in fresh and somewhat contracted specimens. Posteriorly to the ventral sucker the lateral borders run fairly parallel; the posterior end is either pointed or rounded off. The length and breadth vary according to the contraction, being usually 8 to 11 mm. by 1·5 to 2 mm. The suckers are about one-fifth to one-sixth of the length of the body distant from each other, and of about equal size (0·23 to 0·25 mm.). The œsophagus is hardly any longer than the pharynx, which lies close behind the oral sucker; the intestinal cæca reach almost to the posterior border and are often filled with blood. The excretory pore is at the posterior extremity, and the excretory bladder forks in front of the anterior testis. The testes in the posterior fourth of the body lie obliquely one behind the other; the anterior one has four lobes, the posterior one five lobes; the ovary is in the median line transversely, simple or slightly lobed; behind it lies the large pear- or retort-shaped receptaculum seminis and Laurer’s canal. The uterus is in the median field. The vitellaria occupy the fairly broad lateral areas, in about the central third of the body, beginning behind the ventral sucker and terminating at about the level of the ovary; the acini are small and arranged in groups of seven to eight, separated by interstices. The genital pore is close in front of the ventral sucker. The eggs are oval with sharply defined operculum at the pointed pole, 30 µ, by 11 µ. This species, which is frequently confused with others, inhabits the gall-bladder and bile-ducts of the domestic cat especially; but is also found in the dog, in the fox, and in the glutton (_Gulo borealis_). It has been observed in France, Holland, North Germany (being particularly frequent in East Prussia), in Russia, Scandinavia, Siberia, Japan, Tonkin, Hungary, and Italy. The North American form (from cats and _Canis latrans_) is a distinct species (_Opisthorchis pseudofelineus_). In man this species was first found by Winogradoff in Tomsk (nine cases), then by Kholodkowsky in a peasant from the neighbourhood of Petrograd who had travelled a great deal in Siberia, and finally by Askanazy in five persons who were natives of the East Prussian district of Heydekrug. In Tomsk, _Opisthorchis felineus_ is the most frequent parasite of man that comes under observation at _post mortem_ (6·45 per cent.), whereas _Tænia saginata_ has only been found in 3·2 per cent., Echinococcus in 2·4 per cent., _Ascaris lumbricoides_ in 1·6 per cent., and _Oxyuris vermicularis_ in 0·8 per cent. of the autopsies. In the district of Heydekrug, however, the species in question is also frequent, as in a few years five cases came to our knowledge (of which three were diagnosed by the discovery of the eggs in the fæces). [Illustration: FIG. 152.--Egg of _Opisthorchis felineus_, Riv. 830/1.] [Illustration: FIG. 153.--_Opisthorchis felineus_: from the cat. _m._, mouth; _p.b._, pharynx; _i._, gut; _g.p._, genital pore; _ac._, ventral sucker; _ut._, uterus; _v.g._, vitellarium; _ov._, ovary; _s.g._, shell gland; _r.s._, receptaculum seminis; _t._ testes; _ex. p._, excretory pore. (After Stiles and Hassall.)] In none of Winogradoff’s nine cases had the death of the patient been caused direct by the parasites, yet more or less extensive changes in the liver were found in all of them; such as dilatation of the bile-ducts with inflammation and thickening of their walls, and foci of inflammation or atrophy in the liver substance; icterus was present five times and atrophy of the liver an equal number of times; ascites was observed three times, and in two cases, probably of recent date, the organ was enlarged. The number of parasites found fluctuated between a few and several hundreds. In two of Askanazy’s cases, which he examined more closely, carcinoma which had developed at the places most invaded by flukes was found at the _post-mortem_, so that perhaps there may be grounds for the connection which the author seeks to establish between cancer of the liver and the changes induced by the parasites; these changes consist of numerous and even ramified proliferations of the epithelium of the biliary duct into the connective tissue, which is likewise proliferated. The number of worms found in one case amounted to over 100; in a second case, in which the parasites had also invaded the pancreatic duct, their number was even larger. Winogradoff as well as Askanazy found isolated flukes in the intestine also. [Illustration: FIG. 154.--_Opisthorchis pseudofelineus_: from the bile-duct of the cat (Iowa), _m._, oral sucker; _p.b._, pharyngeal bulb; _es._, œsophagus; _i._, intestine; _va._, vagina; _g.p.m._, male orifice; _ac._, ventral sucker; _ut._, uterus; _v.g._ vitellarium; _s.g._, shell gland; _v.dt._, vitelline duct; _ov._, ovary; _r.s._, receptaculum seminis; _L.c._, Laurer’s canal; _t._, testis; _ex.c._, excretory bladder; _ex.p._, excretory pore. (After Stiles.)] Unfortunately, nothing much is known of the history of the development of _Opisthorchis felineus_; we only know that when deposited the eggs already contain a ciliated miracidium, which, however, according to my experience, does not hatch out in water, but only after the entry of the eggs into the intestine of young _Limnæus stagnalis_; no further development, however, occurs. Winogradoff states that he has seen the miracidia hatch after the eggs had been kept in water for a month at 37° C.; and has even observed free miracidia in the bile of man and of a dog respectively. Although the whole post-embryonal development of the cat fluke remains yet to be investigated, Askanazy by a series of experiments on cats and dogs has discovered the mode of infection. The intermediate hosts are fish, and mainly the ide, in this country called Tapar (_Idus melanotus_, H. and Kr.), and of subsidiary importance the roach (_Leuciscus rutilus_). Both species of fish as well as others are readily eaten raw by man on the Courland lagoon (Baltic). It is, moreover, significant that those persons whom Askanazy found infected with the cat fluke were also infected with _Dibothriocephalus latus_, the intermediate host of which is also fish (Lota sp., Esox sp., Perca sp.). In one of his nine cases Winogradoff also saw a small fluke covered all over with spines, which he conjectured to be the young stage of _Opisthorchis felineus_; as, however, according to my experience, this species, even in smaller specimens, is always without spines, the above hypothesis cannot be accepted. It is much more probable that one of the other species that also invade the liver of cats may accidentally be introduced into man; we know, in fact, that _Metorchis albidus_, Braun, and _Metorchis truncatus_, Rud., are both covered with spines. As, however, the spines of the first-named species are rather apt to fall off, and also as it possesses a different shape (spatula-shaped), it may be assumed that probably Winogradoff had found _Metorchis truncatus_, Rud., 1819, in his patient. Genus. *Paropisthorchis*, Stephens, 1912. Structure as in Opisthorchis, except that the ventral sucker and genital pore occur on the apex of a process or pedicle projecting from the anterior portion of the body. This process is about 1/2 mm. long, and is retractile. *Paropisthorchis caninus*, Barker, 1912. Syn.: _Distoma conjunctum_, Lewis and Cunningham, 1872; _Opisthorchis noverca_, M. Braun, 1903 (_pro parte_); _Opisthorchis caninus_, Barker, 1912 (?). Length varies from 2·75 to 5·75 mm. in preserved specimens, average 3·6 to 5·2 mm. Body uniformly spinose, though as a rule spines are not present on the pedicle. Body slightly concavo-convex, the concavity being ventral. Oral sucker 0·28 mm. Pharynx 0·224 by 0·184 mm. Œsophagus 0·04 mm. Ventral sucker 0·176 mm. in diameter. Pedicle about 1/2 mm. long, may be completely retracted. _Genital Pore_--opens on the apex of the pedicle in front of the ventral sucker. Its exact position varies with the state of contraction of the parts. In certain cases it actually opens within the cuticular border of the sucker, in other cases it opens externally to the sucker and anterior to it. The opening is covered with scales. The vas deferens and uterus run alongside one another until they merge near the apex of the pedicle into a common sinus. _Vitellaria_--consist of eight acini on each side, extending from slightly behind the base of the pedicle to the anterior border of the ovary, or as far back as a line separating the posterior border of the ovary from the anterior border of the anterior testis. [Illustration: FIG. 155.--_Paropisthorchis caninus_: from the bile-ducts of the pariah dog, India. _Acet. v._, ventral sucker; _Ut._, uterus; _V. ex. lat_., longitudinal excretory duct; _V. sem._, seminal vesicle; _Sem. rec._, seminal receptacle; _Ov._, ovary; _V. ex._, excretory bladder; _Test. l._, left testis; _Test. r._, right testis; _P. ex._, excretory pore. × 40. (After Stephens.)] _Testes._--Anterior testis 0·496 by 0·44 mm.; posterior testis 0·52 by 0·48 mm., usually ovoid, though both may be regularly lobed. The anterior testis is usually on the left side. _Ovary_--multilobular, the lobes 6 to 8 being irregular in size and shape. _Shell Gland_--extensive and diffuse, occupying an area which approximately corresponds with the loop of the transverse vitelline ducts. _Seminal Receptacle_--globular, to the right of and dorsal to the posterior lobe of the ovary. _Laurer’s Canal_--generally runs from the end of the receptacle with a single curve medially and backwards. _Uterine Coils_--form loosely packed transverse coils terminating slightly in front of the level of the first vitelline acini. From here the uterus passes forwards into the pedicle to the left and ventral to the seminal vesicle. _Seminal Vesicle_--commences about the level of the first vitelline acini. The coils displace the uterus ventrally and to the left. In the pedicle the vesicle diminishes in extent and lies in its dorsal (anterior) side. _Habitat._--Liver of pariah dogs, India. In North-Western Provinces about 40 per cent. are infected. This fluke appears to be different from _Amphimerus_ (_Opisthorchis_) _noverca_ in man, as the latter has not the pedicle on the summit of which lie the sucker and common genital pore. Genus. *Amphimerus*, Barker, 1912 (?). Structure as in Opisthorchis, except that the vitellaria are separated into two portions, an ant-ovarial and a post-ovarial. [Illustration: FIG. 156.--_Amphimerus noverca_, Braun. o.s., oral sucker; p.b., pharynx; ac., ventral sucker; ut., uterus; v.g., vitellarium; ov., ovary; v.d., vas efferens; ex.c., excretory canal; t., testis. (After McConnell.)] *Amphimerus noverca*, Barker, 1912 (?). Syn.: _Distomum conjunctum_, McConnell, 1876 (_nec_ Cobbold, 1859); _Opisthorchis noverca_, M. Braun, 1903 _pro parte_. At the autopsy of two Mahommedans who died in Calcutta, McConnell found a large number of Distomata in the thickened and dilated bile-ducts. The worms were lancet-shaped, covered with spines, and measured 9·5 to 12·7 mm. in length and 2·5 mm. in breadth. The two suckers lie very close to one another, the anterior one being larger than the ventral; the genital pore opens immediately in front of the ventral sucker; pharynx spherical; intestinal cæca extending far back. At the commencement of the posterior third of the body the two testes, somewhat apart, the anterior one roundish, the posterior one distinctly lobed. The transverse and slightly lobed ovary in front of the bifurcation of the *Y*-shaped excretory bladder, whence the uterus, in convolutions barely spreading beyond the central field, extends to the pore; the vitellaria in the lateral areas commence behind the ventral sucker and extend to the testes. Cirrus pouch absent. Eggs oval, 34 µ by 21 µ. Genus. *Clonorchis*, Looss, 1907. Structure as in Opisthorchis, distinguished, however, by the branched testes situated one behind the other, the branches of which ventrally encroach upon the gut forks; dorsal to the testes the *S*-shaped excretory bladder, the main branches of which, arising at the level of the bifurcation of the gut, open into the bladder below its anterior end. Parasitic in the bile-ducts of mammals and man. [Illustration: FIG. 157.--_Metorchis conjunctus_,[272] (Syn.: _Distomum conjunctum_, Cobb., _nec_ Lew. and Cunn., _nec_ McConn.): from _Canis fulvus_. _Vs._, ventral sucker; _I._, intestine; _Vsc._ vitellaria; _Ex._, excretory bladder; _T._, testes; _O._, ovary; _Ms._, oral sucker; _Ph._, pharynx; _Ut._, uterus. (After Cobbold.)] [272] This species from _Canis fulvus_ was for long thought to be the same as that here described as _Amphimerus noverca_. It probably does not belong to the genus Metorchis. *Clonorchis sinensis*, Cobbold, 1875. Syn.: _Distoma sinense_, Cobbold, 1875; _Distoma spathulatum_, R. Leuckart, 1876 (_nec_ Rudolphi, 1819); _Distoma hepatis innocuum_, Baelz, 1883. In shape resembles _Opisthorchis felineus_, 13 to 19 mm. long, 3 to 4 mm. broad, at the beginning of sexual maturity 12 to 13 mm. long, 2·5 to 3 mm. broad. Oral sticker 0·58 to 0·62 mm., ventral sucker 0·45 to 0·49 mm. in transverse diameter. In the parenchyma numerous yellowish or brownish granules, especially behind the oral sucker and at the posterior end. Testicular branches very long, in the anterior testis often four, in the posterior testis five branches. Ovary generally with three large lobes and a smaller lobe. Vitellaria not always symmetrical, generally extending laterally from the ventral sucker to the ovary, interrupted in parts. Eggs 26 µ to 30 µ by 15 µ to 17 µ. Average 29 µ by 16 µ. [Illustration: FIG. 158.--_Clonorchis sinensis._ _C.L._, Laurer’s canal; _Dst._, vitellaria; _Ex._, excretory bladder; _H._, testes; _K._, ovary; _R.s._, receptaculum seminis; _Vd._, terminal section of vas deferens. Magnified 4-1/2 times. (After Looss.)] [Illustration: FIG. 159.--Ova of _Clonorchis sinensis_. The knobs on the ends of the eggs are not shown. 900/1. (After Looss.)] This (?) species was discovered in 1874 by McConnell, in Calcutta, in the bile-ducts of a Chinaman who died shortly after being admitted into hospital. _Habitat._--Bile-ducts of man, dog and cat. _Distribution._--Especially in China, apparently rare in Japan. *Clonorchis endemicus*, Baelz, 1883. Syn.: _Distoma sinense_ s. _spathulatum p.p._; _Distoma hepatis endemicum_ s. _perniciosum_, Baelz, 1883; _Distoma japonicum_, R. Blanchard, 1886. Very similar to the previous species and consequently generally confused with it. Length between 6 and 13 mm., width varying between 1·8 and 2·6 mm. Oral sucker 0·37 to 0·5 mm., usually 0·43 to 0·45 mm. in transverse diameter; ventral sucker 0·33 to 0·45 mm., usually 0·37 to 0·40 mm. No pigment in parenchyma; anterior testis with four, posterior testis with five branches. Vitellaria continuous, ova 26 µ by 13 µ to 16 µ. _Habitat._--Bile-ducts of man, dog, cat and pig. _Distribution._--This species occurs very frequently in man, in certain districts of Japan, especially in the province of Okayama, Central Japan, in particular localities of which above 60 per cent. of the population are infected. The worms are sometimes found in enormous numbers in the liver (upwards of 4,000), also in the pancreas and rarely in the duodenum. It is common in Tonkin and Indo-China. Léger in Tonkin found 50 per cent. of people apparently in normal health infected, so that probably symptoms only arise when the infection is intense. [The exact distribution of these two species is, however, not precisely defined at present, as commonly no distinction is made between them.--J. W. W. S.] [Illustration: FIG. 160.--_Clonorchis endemicus._ × 6 about. (After Looss.)] [Illustration: FIG. 161.--_Clonorchis endemicus_: eggs. The knobs on the eggs are not shown. × 900. (After Looss.)] Verdun and Bruyant deny, in opposition to Looss, the possibility of being able to distinguish within the genus Clonorchis the two species described, but they admit the justification for the new genus. They also report the occurrence of _Opisthorchis felineus_ in man in Tonkin (_Compt. Rend. Soc. de Biol._, lxii, 1907). _Pathology._--Both species of Clonorchis give rise to grave symptoms. The liver is generally enlarged, though when the infection has lasted some time it begins to contract. The surface of the organ is studded with white vesicles, and on cutting into it one sees numerous cavities with thickened walls (distended bile-ducts) filled with a brownish fluid containing innumerable eggs, which cause its colour. Microscopically, the epithelium of the bile-ducts is either (1) entirely destroyed, or (2) actively proliferates, forming an adenomatous outgrowth. Occasionally this proliferation is not limited by the wall of the bile-duct but penetrates it and leads to a growth of numerous new ducts, forming a malignant biliary adenoma. The bile-ducts have their connective tissue wall greatly sclerosed. These fuse with one another, forming areas of sclerosis devoid of liver tissue. As a result of these changes the liver cells atrophy and undergo fatty pigmentary and granular degeneration. Besides these changes, due probably to the toxic action of the flukes, mechanical obstruction due to the actual plugging of the ducts by the flukes causes retention of bile and icterus, and through pressure on veins, ascites and hypertrophy of the spleen. To what extent blood or bile respectively forms the food of the flukes is uncertain. _Life-history._--(Kobayashi, 1911, _Mitteilungen aus dem kaiserlichen Institut für Infektions-Krankheiten zu Tokio_, pp. 58–62.) It results from the work of Kobayashi in Japan that fresh-water fish form the _second_ intermediate host for _Clonorchis endemicus_. He fed cats with encysted flukes (cercariæ) from various fish and easily succeeded in infecting them, _e.g._ a kitten, proved to be uninfected by repeated examination of its fæces, was fed on infected fish; a month later innumerable flukes were found in the bile-ducts, gall-bladder, pancreas and even in the duodenum. The fish infected were _Leucogobis güntheri_, _Pseudorasbora parva_, and to a less extent _Acheclognathus lanceolata_, _Acheclognathus limbata_, _Paracheclognathus rhombea_, _Pseudoperilampus typus_, _Abbottina psegma_, _Biwia zezera_ and _Sarcocheilichthys variegatus_. The cysts occur throughout the muscles and subcutaneous tissue of the fish. Length 0·13 mm., breadth 0·1 mm. The cercaria lies folded in the cyst, length 0·5 mm. breadth 0·1 mm. It tapers posteriorly. Skin at first covered with fine spines, disappearing as they grow older. Body dotted with fine pigment. The _first_ intermediate host is still unknown. Sub-family. *Metorchiinæ*, Lühe, 1909. Genus. *Metorchis*, Looss, 1899, emend. auctor. Hind end rounded. Gut forks reach extreme end. Testes only slightly lobed, filling the hind end. *Metorchis truncatus*, Rud., 1819. This species, which attains a length of 2 mm., is slender and conical, the anterior end is pointed and the posterior truncated, and provided with a muscular tuberosity that resembles a terminal sucker; for this reason the discoverer of the species (Rudolphi) classed it with the Amphistomes. The cuticle in the young, as well as in the adult specimens, is entirely and closely covered with spines. Suckers about equal in size (0·134 to 0·172 mm.); the ventral sticker lies somewhat in front of the middle of the body. The pharynx is small (0·09 mm.), the œsophagus minute, the intestinal cæca reach to the posterior extremity. Between them, and in front of their blind ends, lie the two elliptical testes, one generally a little in front of the other. In front of them, either in the median line or somewhat laterally, the spheroidal ovary is situated; in front, again, is the uterus, the coils of which usually extend beyond the median field. The vitellaria are at the sides of the central third of the body, thus commencing in front of the ventral sucker; cirrus pouch absent; the genital pore is close in front of the acetabulum. The excretory pore is terminal (?). Eggs 29 µ by 11 µ. _Metorchis truncatus_ lives in the bile-ducts of the seal, cat, dog, fox, and glutton (_Gulo borealis_). The source of infection is unknown, although one would suspect fish. Askanazy did not succeed in getting this fluke in his feeding experiments, but another species, _Metorchis albidus_, not uncommon in cats by feeding them on roach (_Leuciscus rutilus_). [Illustration: FIG. 162.--_Metorchis truncatus_, Rud.: from the biliary ducts of the domestic cat. _V.s._, ventral sucker; _I._, gut; _V.sc._, vitellaria; _T._, testes; _O._, ovary; _R.s._, receptaculum seminis; _Ut._, uterus. 25/1.] Family. *Heterophyiidæ*, Odhner, 1914. Genus. *Heterophyes*, Cobbold, 1866. Syn.: _Cotylogonimus_, Lühe, 1899; _Cænogonimus_, Looss, 1899. No crown of spines on head. Body divided into a narrow, movable, anterior part (neck), and a broader, less movable, posterior portion, which contains the genitalia. The suckers separated from one another by a space equal to half the length of the body or more; the pharynx is close behind the oral sucker; the œsophagus is long; the intestinal cæca extend to the posterior border; the genital pore is placed laterally, and behind the ventral sucker. Genital sucker provided with a circlet of chitinous rodlets, shaped like stags’ horns. The testes are at the posterior end, the ovary in a median position in front of them. Laurer’s canal with receptaculum seminis present; the small vitellaria are at the sides of the posterior part of the body. Parasitic in the intestine of mammals and birds. *Heterophyes heterophyes*, v. Sieb., 1852. Syn.: _Distomum heterophyes_, v. Siebold, 1852; _Heterophyes ægyptica_, Cobbold, 1866; _Mesogonimus heterophyes_, Railliet, 1890; _Cœnogonimus heterophyes_, Looss 1900; _Cotylogonimus heterophyes_, Braun, 1901. Length up to 2 mm., breadth 0·4 mm.; the neck not sharply defined; in life it stretches to double the length of the hind body. The scales are rectangular, 5 µ to 6 µ by 4 µ, their posterior margin serrate with seven to nine teeth. Cuticular glands are numerous on the ventral surface, especially in the fore part of the body, and partly discharge at the anterior border of the oral sucker. The oral sucker is 0·09 mm., the ventral sucker 0·23 mm. in diameter; the pharynx measures 0·05 to 0·07 mm. in length; the œsophagus is about three times as long; posteriorly the intestinal cæca are directed one towards the other and terminate beside the excretory bladder. Close in front of the posterior ends of the intestinal branches are the two elliptical testes, which are not exactly on the same level. In the middle in front of them is the receptaculum seminis, and in front of the latter lies the spherical or elliptical ovary. The two vasa efferentia unite to form the vas deferens, which after a short course passes over into the angularly bent seminal vesicle; after the entry of the prostatic glands it becomes united with the metraterm (vagina), and the common duct opens into the genital sucker. The latter is somewhat smaller than the ventral sucker, lateral to and close (0·15 mm.) behind it, and bears a not entirely closed ring of from seventy-five to eighty chitinous rods (20 µ in length). The vitellaria on either side consist of about fourteen acini. The uterus is spread almost throughout the entire posterior part of the body. The eggs have thick shells with a knob resembling that of Clonorchis eggs but not so prominent, and measure 30 µ by 17 µ; they contain a completely ciliated miracidium with a rudimentary intestinal sac. [Illustration: FIG. 163.--_Heterophyes heterophyes_, v. Sieb. _C._, cerebral ganglion; _I._, intestinal cæca; _Ct.g._, cuticular glands; _V.sc._, vitellaria; _Ut._, genital sucker; _T._, testes--the excretory bladder between them; _L.c._, Laurer’s canal; _R.s._, receptaculum seminis, with the ovary in front of it; _G.c._, ventral sucker; _Vs._, vesicula seminalis, 53/1. On the left side above, an egg, 700/1, is depicted, and below it three chitinous rodlets from the genital sucker. 700/1. (After Looss.)] This species was discovered in 1851 by Bilharz in the intestine of a boy who died in Cairo; a second case was only found in 1891 and published by R. Blanchard, so that it appeared as if the species were very scarce. According to Looss, this is, however, not the case, but the species easily escapes notice on account of its small size. Looss found it in Alexandria twice in nine autopsies, and once in Cairo, and has recently stated that in man “it is not at all uncommon to meet with the parasite in cadavers, and the eggs of the worm in the stools of the patients.” Leiper records one case from Japan and one from China. The parasites occupy the middle third of the small intestine, and even when present in large numbers appear to be harmless. This small species, according to Looss, frequently occurs in Egyptian dogs, less so in cats, and has also been found in the fox, as well as once in _Milvus parasiticus_; Janson also reports this species from the intestine of the dog in Japan. *Metagonimus*, Katsurada, 1913; Yokogawa, Leiper, 1913. Resembles in general structure Heterophyes. In the arrangement of its ventral genital suckers resembles but differs from that of Tocotrema,[273] Looss. The ventral and genital suckers lie laterally and on the right. [273] In the genus Tocotrema the common genital duct opens into the ventral sucker. *Metagonimus yokogawai.* Katsurada, 1913. Syn.: _Yokogawa yokogawai_, Leiper, 1913. [Illustration: FIG. 164.--_Metagonimus yokogawai_, Katsurada, 1913: the spines are only shown over a small part of the skin. (After Leiper.)] One to 1·5 mm. long, seldom 2·5 mm., and 0·4 to 0·7 mm. broad; elliptical in shape. The body is thickly covered with nail-shaped spines about 10 µ long. Oral sucker 77 µ, to 85 µ in diameter. Ventral sucker characteristic and peculiar 0·12 to 0·14 mm. by 0·08 to 1 mm. It is a sac-like organ placed deeply in the body, but does not open as in other flukes on the ventral surface. Testes elliptical, not quite symmetrically placed at the hind end of the body. Vesicula seminalis retort-shaped, situated transversely, internal to the ventral sucker. Pars prostatica present. Ejaculatory duct opens with the uterus into a genital sinus, which, together with the internal opening of the ventral sucker, opens into a pit at the front of the ventral sucker. The opening of the genital sinus and that of the ventral sucker are furnished with a complex muscular apparatus. Ovary spherical, 0·12 to 0·13 mm. in diameter, lies in the middle of the hind body. Receptaculum seminis and Laurer’s canal present. Vitellaria in the hind half of the body, consisting of about ten acini on each side. Shell gland to the left of the ovary. Uterus forms three to four transverse coils. Eggs elliptical, double contoured, yellowish-brown in colour. There is no shoulder below the operculum as in the eggs of _Cl. sinensis_. At the rounder end there is a thickening or knob different from the spine-like or hook-like process seen in _Cl. sinensis_. Dimensions 28 µ by 16 µ. _Habitat._--Mainly in upper or middle portion of jejunum, rarely in cæcum. They penetrate deep into the mucosa, but not into the submucosa, and _post mortem_ appear as a number of small brown points. They frequently occur in the solitary glands, which they destroy. They cause chronic catarrh of the gut. Parasitic in man and mammals. _Geographical Distribution._--Japan. _Life-history._--The cercarial stage occurs in a trout (_Plecoglossus altivelis_) and seldom in Crassius sp. and Cyprinus sp. Infection takes place through the eating of the fish raw. Seven to sixteen days later eggs appear in the fæces (of dog). Family. *Dicrocœliidæ*, Odhner, 1910. Genus. *Dicrocœlium*, Dujardin. _Dicrocœliidæ_, with leaf-shaped bodies, pointed posteriorly and anteriorly. Greatest width behind the mid-line. Vitellaria double. The testes smooth or indented, lying symmetrically or obliquely beside or behind the ventral sucker. The ovary approaches the median line behind one testis. Parasitic in the liver and gall-bladder (rarely in the intestine) of members of all classes of vertebrate animals--by preference in birds and mammals. [Illustration: FIG. 165.--_Dicrocœlium dendriticum_, Rud. _V.s._, ventral sucker; _Cb._, cirrus pouch; _I._, intestinal cæca; _V.sc._, vitellaria; _T._, testicles; _O._, ovary; _M.s._, oral sucker; _Ut._, uterus. 15/1.] *Dicrocœlium dendriticum*, Rud., 1819. Syn.: _Dicrocœlium lanceatum_, Stil. and Hass., 1896; _Fasciola lanceolata_, Rud., 1803 (_nec_ Schrank, 1790); _Distomum lanceolatum_, Mehlis, 1825; _Dicrocœlium lanceolatum_, Dujardin, 1845. [Illustration: FIG. 166.--Eggs of _Dicrocœlium dendriticum_, Rud. To the left seen flat, to right lying on one side. 600/1.] [Illustration: FIG. 167.--Miracidia of _Dicrocœlium dendriticum_. _a_, from the dorsum; _b_, from the side. (After Leuckart.)] Body lancet-shaped, narrowing especially at the anterior extremity; length 8 to 10 mm., breadth 1·5 to 2·5 mm., the greatest breadth usually behind the middle of the body. Suckers distant from each other by about one-fifth the length of the body; oral sucker about 0·5 mm., ventral sucker about 0·6 mm. Pharynx globular, adjoining the oral sucker; œsophagus 0·6 mm. in length; intestinal cæca reach to four-fifths of the body length. Genital pore at the level of the bifurcation of the intestine; cirrus pouch small and slender. The large, slightly lobed testes lie obliquely one behind the other behind the ventral sucker; the ovary, which is considerably smaller, is placed behind the posterior one; the vitellaria, commencing at the level of the posterior testis, terminate far before the cæca. The uterus, situated behind the ovary, extends throughout the posterior end, not confined to the central field, but overlapping the lateral fields with its transverse coils; at the posterior edge of the body it turns back again and winds forwards to the ovary in transverse loops, then between the testes, and finally, dorsal to the ventral sucker, terminates in the genital pore. The thick-shelled eggs when young are yellowish, when older dark brown. They measure 38 µ to 45 µ by 22 µ to 30 µ. They contain an oval or roundish miracidium, only the anterior part of which is ciliated, and which possesses a rudimentary intestinal sac with a boring spine. The miracidia do not hatch out in water spontaneously, but, according to Leuckart, in the intestines of slugs (_Limax_, _Avion_), but they do not develop either in these (slugs) or in water-snails. The lancet fluke inhabits the biliary duct of herbivorous and omnivorous mammals (sheep, ox, goat, ass, horse, deer, hare, rabbit, pig), and is often found associated with the liver fluke; it is not, however, so common nor so widely disseminated, nevertheless, it has been met with outside of Europe, namely, in Algeria, Egypt, Siberia, Turkestan, and North and South America. In man it is still more uncommon than the liver fluke, and has hitherto only been observed seven times (Germany, Bohemia, Italy, France, and Egypt); it may, however, have occurred more frequently, and have been overlooked, as in slight infections it produces no special symptoms. The intermediate host is still unknown. Leuckart for some time held the opinion that small species of _Planorbis_ from fresh water, which contain encysted Distomata, were to blame, and he supported his views by a feeding experiment which seemingly yielded positive results; this, however, is not definitely proved. Piana’s statement that small land snails are the intermediate hosts has also not been proved. Family. *Echinostomidæ*, Looss, 1902. Sub-family. *Echinostominæ*, Looss, 1899. Genus. *Echinostoma*, Rud. 1809; Dietz, 1910. Fore-body not bulging. Greatest width at or behind the ventral sucker. Oral sucker not atrophied. Collar kidney-shaped with a double dorsally unbroken row of spines, terminating in four to five angle spines. The border spines of the aboral series not larger than the oral. Skin spined or smooth. Body elongated. Uterus long with numerous transverse coils. Ventral sucker in the anterior quarter of body. Cirrus sac small, almost completely in front of the ventral sucker. Testes round or oval, smooth incurved or lobed, in the hinder half of body. Ovary median or lateral in front of testes. Vitellaria from hinder margin of ventral sucker to end of body. Eggs oval, 84 µ to 126 µ by 48 µ to 82 µ. The spines placed most ventrally, or those placed most medially on ventral surface, are from differences of position or form termed “angle” spines, the rest “border” spines. _Type._--_Echinostoma echinatum_, Rud. *Echinostoma ilocanum*, Garrison, 1908. Length 4 to 5 mm., breadth 1 to 1·35 mm., thickness 0·5 to 0·6 mm. The circum-oral disc 0·3 mm. broad, separated by a shallow groove from the body. Crown of forty-nine spines and five to six angle spines on each side continuous with an irregularly alternating series of fourteen spines on the dorsum. Largest spines are 34 µ long, 8 µ thick at the base. The remainder of the dorsal spines are 24 µ by 6 µ. Skin thickly covered with scales on the margins of the body as far back as the level of the hind testis. Oral sucker, 0·18 mm.; ventral sucker, 0·4 to 0·46 mm. Its anterior border about 0·07 mm. from the anterior end. Pharynx 0·17 mm. long, 0·11 mm. broad. Testes about mid-line of the body, much lobed; the lobes of the anterior testis run transversely, while the axis of the posterior testis is longitudinal, as often occurs in the _Echinostomidæ_. Cirrus sac reaches to the centre of the ventral sucker. Ovary transversely oval in front of the testes. Vitellaria commence about half-way between the ventral sucker and ovary and extend to the posterior end. Eggs numerous, 92 µ to 114 µ by 53 µ to 82 µ. _Average._--99·5 µ by 56 µ. _Habitat._--Gut of man (Filipinos), Philippine Islands. [Illustration: FIG. 168.--_Echinostoma ilocanum._ _Vo._, oral sucker; _Ph._, pharynx; _Cirre_, cirrus; _V.v._, ventral sucker; _Ut._, uterus; _G.c._, ovary; _Ov._, shell gland; _T._, testes; _T.d._, vitellarium; _C.ex._, excretory vesicle. (After Brumpt.)] [Illustration: FIG. 169.--_Echinostoma ilocanum_, Garrison, 1908: head end showing collar of spines, ventral view. (After Leiper.)] *Echinostoma malayanum*, Leiper, 1911. Twelve millimetres long, 3 mm. broad, 1·3 mm. thick. Ends bluntly rounded. At the anterior end a ventral furrow on either side, one-third the width of the body, marking off the circum-oral collar. Along its edge is a row of forty-three spines extending across the middle line dorsally but not ventrally. The spines vary in size from 0·07 mm. in length (ventrally) to 0·05 to 0·016 mm. (dorsally). Cuticular spines also exist on the ventral side as far back as posterior end of body, but dorsally limited to a triangular area ending in front of the ventral sucker. Oral sucker 0·07 mm. thick, occupying the middle third of the circum-oral disc; pharynx 0·25 mm. in diameter; œsophagus 0·04 mm. long; gut cæca simple, extending to end of body; ventral sucker 0·9 mm. long by 0·75 mm. broad by 0·7 mm. deep; wall about 0·25 mm. thick. The sucker is inclined at an angle of 40° to the ventral surface. Testes lobed, one behind the other, behind the ventral sucker. Cirrus pouch well developed, reaching to the posterior edge of the sucker. Genital pore in the angle between neck and anterior lip of ventral sucker. Ovary smooth, 0·3 mm. in diameter, 0·85 mm. behind ventral sucker. Vitellaria very numerous, extending from posterior margin of sucker to posterior end of body, where they intermingle. Eggs few in number, brown and large. _Habitat._--Gut of man (Tamils), Malay States. [Illustration: FIG. 170.--_Echinostoma malayanum_, Leiper, 1912: anterior end showing collar of spines, ventral view. (After Leiper.)] Sub-family. *Himasthlinæ*, Odhner, 1910. Genus. *Artyfechinostomum*, Clayton-Lane, 1915. Crown of thirty-nine spines, continuous over dorsum. Two corner spines long. Vitellaria extend from posterior margin of sucker to posterior end of fluke. Eggs without filament. [Although the possession of strong rose-thorn hooks is given by Odhner as a sub-family characteristic, yet in this genus assigned to this sub-family they have not been seen.--J. W. W. S.] *Artyfechinostomum sufrartyfex*, Clayton-Lane, 1915. Spirit specimens: 9 by 2·5 by 0·8 mm. thick. Ventral sucker conspicuous, 1 mm. in diameter. Cirrus sac 2 mm. long. Testes lobed, about 1·5 mm. in diameter. Posterior border of posterior testes 1 mm. from posterior end. Vitellaria meet posteriorly behind the posterior testis. Family. *Schistosomidæ*, Looss, 1899. Genus. *Schistosoma*, Weinl, 1858. Syn.: _Gynæcophorus_, Dies., 1858; _Bilharzia_, Cobb., 1859; _Thecosoma_, Moq. Tandon, 1860. The males have bodies that widen out considerably behind the ventral sucker, the lateral parts of which in-roll ventrally, forming the almost completely closed canalis gynæcophorus, within which the female is enclosed. There is no cirrus pouch. The male has five or six testes, the females are filiform; the uterus is long. There is no Laurer’s canal. The ova almost equally attenuated at either extremity; they have a small terminal spine, and are not provided with a lid. They contain a miracidium, ciliated on all sides, which is characterized by the possession of two large glandular cells, which discharge anteriorly beside the gastric sac. They live in the vascular system of mammals. (An allied genus [Bilharziella] lives in the blood-vessels of birds.) *Schistosoma hæmatobium*, Bilharz, 1852. Syn.: _Distoma hæmatobium_, Bilh.; _Distoma capense_, Harley, 1864. [Illustration: FIG. 171.--_Schistosoma hæmatobium_, Bil.: male carrying the female in the canalis gynæcophorus. 12/1. (After Looss.)] _The Male_ is whitish, 12 to 14 mm. in length, but is already mature when 4 mm. long. The anterior end is 0·6 mm. or a little over in length. The suckers are near each other, the oral sucker is infundibular, and the dorsal lip is longer than the ventral one. The ventral sucker is a little larger, 0·28 mm., and is pedunculated. A little behind the ventral sucker the body broadens to a width of 1 mm., decreasing, however, in thickness; the lateral edges in-roll ventrally, so that the posterior part of the body appears almost cylindrical, 0·4 to 0·5 mm. in diameter; the posterior extremity is somewhat more attenuated. The dorsal surface of the posterior part of the body is covered with spinous papillæ. There are delicate spines on the suckers, and larger ones invest the entire internal surface of the gynæcophoric canal, as well as a longitudinal zone at the edge of that side of the external surface that is covered by the other side rolling over it. The œsophagus is beset with numerous glandular cells (fig. 173), and presents two dilatations; the intestinal bifurcation is close in front of the ventral sucker, the two branches uniting sooner or later behind the testes into a median trunk, which may again divide at short intervals. The excretory pore is at the posterior end, but placed somewhat dorsally; the genital pore is at the beginning of the gynæcophoric canal, thus behind the ventral sucker; into it opens the vas deferens which, posteriorly, broadens into the seminal vesicle and then continues as the vasa efferentia of the four or five testes (fig. 173). [Illustration: FIG. 172.--Transverse section through a pair of _Schistosoma hæmatobium_ in copulâ. In the male the point of reunion of the intestinal forks has been cut across. (After Leuckart.)] [Illustration: FIG. 173.--Anterior end of the male _Schistosoma hæmatobium_, Bilh. _V.s._, ventral sucker; _I._, gut cæca; _G.p._, genital pore; _T._, testes; _O.s._, oral sucker; _Oe._, œsophagus with glandular cells; _V.s._, vesicula seminalis. 40/1. (After Looss.)] _The Female_--filiform, about 20 mm. in length, pointed at each end, and measuring 0·25 mm. in diameter in the middle. Their colour varies according to the condition of the contents of the intestine. (Posteriorly they are dark brown or blackish.) The cuticle is smooth except in the sucker, where there are very delicate spines, and at the posterior end, where there are other larger spines. The oral sucker is a little larger than the pedunculated ventral sucker (0·07 and 0·059 mm. respectively). The anterior part of the body, 0·2 to 0·3 mm. in length; the œsophagus is as in the male. The intestinal bifurcation is in front of the ventral sucker, the two branches uniting behind the ovary and the trunk running in a zigzag manner to the posterior border. There are indications of diverticula at the flexures. The ovary is median. In young females it is of an elongated oval shape; in older females the posterior end becomes club-shaped, whereas the anterior end becomes attenuated; the oviduct originates at the posterior end, but immediately turns forwards and joins the parallel vitelline duct in front of the ovary (fig. 174), where the shell gland cells open; the common canal becomes dilated to form the oötype, and then proceeds as the uterus, with only slight convolutions, along the central field to the genital pore, which lies in the middle line immediately behind the ventral sucker. The single vitellarium starts behind the ovary and extends to the posterior end. The acini are situated at the sides of the excretory duct, which runs a median course. The eggs are compact spindles, much dilated in the middle; they have no lid, and are provided with a terminal spine (rudimentary filament) at the posterior end, measuring 120 µ to 150 µ in length and 40 µ to 60 µ in breadth, but vary in size and shape (fig. 175). _Distribution._--In order to understand the distribution of the worms and eggs in the body, it may be well to recall the blood supply of the abdominal and pelvic organs. It is generally assumed that the early life (? cercarial stage) of the worms occurs in the liver, and that the young worms travel from here, where they are invariably found, to their various sites along the portal vein and its tributaries and so _against_ the blood stream. The tributaries of the portal vein are:-- (1) _Superior mesenteric_, the tributaries of which are: (_a_) the veins of the small intestine; (_b_) ileo-colic; (_c_) right colic; (_d_) middle colic; (_e_) right gastro-epiploic; and (_f_) inferior pancreatic. By these paths infection of the small intestine, ascending and transverse colon and pancreas would occur. (2) _Splenic._ (Ova have been recorded by Symmers in the spleen.) (3) _Inferior mesenteric_, the tributaries of which are (_a_) superior hæmorrhoidal veins from the upper part of the hæmorrhoidal plexus; (_b_) sigmoid veins from sigmoid flexure and lower portion of _descending_ colon; (_c_) left colic vein draining descending colon. The superior hæmorrhoidal veins form a rich plexus in the rectum, and below this level in the upper and middle parts of the anal canal. The plexus forms two networks, an _internal_ plexus in the submucosa and an external on the outer surface. The _internal_ plexus opens at the anal orifice into: (_a_) branches of the inferior hæmorrhoidal vein (from the pudic); (_b_) the external plexus. The _external_ plexus gives off: (_a_) inferior hæmorrhoidal opening into internal pudic (of _internal iliac_ vein); (_b_) mid-hæmorrhoidal into _internal iliac_ or its branches; and (_c_) superior hæmorrhoidal opening into inferior mesenteric. The external plexus further communicates with the vesico-prostatic plexus. The vesico-prostatic (vaginal) plexus opens into the _vesical veins_, which drain into the interior iliac vein. This plexus also receives afferents from the pudendal plexus, the chief tributary of which is the dorsal vein of the penis. The pudendal plexus also receives branches from the inferior pudic and the anterior surface of the bladder. There is thus a communication between the portal vein and the vena cava by means of these plexuses, _viz._, through the inferior and middle hæmorrhoidals, and by the inferior hæmorrhoidals to the bladder and thence by the vesical veins or the pudic to the caval system (interior iliac). It is thus by the inferior mesenteric and its tributaries that the worms reach the descending colon, rectum, anal canal, and eventually the bladder, and in some cases the caval system. Before considering what is actually found _post mortem_ in these veins and the organs drained by them, we may further recall the fact that the calibre of “medium” veins is 4 to 8 mm., “small” veins less than 40 µ in diameter and capillaries 8 µ to 20 µ. Further, the maximum diameter of the male worm is 1 mm., that of the female 280 µ and eggs _in utero_ 80 µ to 90 µ long by 30 µ to 40 µ. _Liver and Portal Vein._--Here worms are most easily found _post mortem_. Often only males are found and these of the same size, and if females occur only a few worms are found in copulâ. The worms are frequently not full size and the males may contain no free spermatozoa in their testes, and as regards the females some may be fertilized, others not, as shown by the presence or absence of spermatozoa in the seminal receptacle or uterus. In either case they may contain eggs--_lateral-spined_--usually one, less often two, but there may be as many as five or six. These eggs may also show some abnormality, which takes the form of: (1) abnormal contents, _viz._, disintegrating yolk cells with or without an ovarian cell; (2) abnormal shape but with normal contents and probably represented by the collapsed and empty egg-shells which are found in the tissues. As to the interpretation of these facts, Looss believes that these lateral-spined eggs are products of young females whose egg-laying is not at first properly regulated. The shape that the eggs take, _viz._, with a lateral spine, is determined by an excess of material--ovarian and yolk cells--being present in the oötype. The shape of eggs depends upon the position they have in the oötype during their formation. In young females an excess of cells--yolk cells especially--accumulates, distending not only the dorsal wall but a portion also of the short duct joining the oötype to the uterus. The result of this is that the axis of the oötype and egg is almost transverse to the body, and the posterior funnel-shaped portion of the oötype, instead of being terminal, has now a lateral or rather a ventral position, so that the spine which occupies this portion, instead of being terminal, is now lateral. It is noteworthy that these lateral-spined eggs are thicker, owing to the excess of material present, and not uncommonly have a curved anterior border, due to a projection of the anterior end into the anterior opening of the oötype. As these eggs are being laid by females in the portal vein they are carried back to the liver by the blood stream. The liver is one of the commonest sites for these eggs; also terminal-spined eggs may be found here for the same reason. _Hæmorrhoidal Veins._--Mature worms, generally in copulâ, are usually found here, though young not fully grown females may also occur. The tissues of the rectal wall (or colon) show, as a rule, large quantities of lateral-spined eggs, though less often only terminal-spined eggs may be found. _Vesico-prostatic Plexus._--Worms in copulâ are found in the veins of the submucosa in the bladder, and the eggs in the mucosa, and those voided are usually terminal-spined, though lateral-spined eggs are not so rare as generally thought. The problem next arises as to how the eggs get to the lumen of the gut or bladder. The female worm is 280 µ in diameter. Veins in the submucosa of the rectum less than 178 µ in diameter are not affected with endophlebitis. It is probable that the female even by stretching could not penetrate much beyond this. Eggs are probably then laid in the submucosa as near the muscularis mucosa as possible. Now if the eggs are laid in a vein of larger calibre than the worm fills, the eggs would be carried back to the inferior mesenteric vein, so that presumably the worm must succeed in blocking the vein already narrowed by endophlebitis, so that by the stasis which ensues the eggs may escape from the veins. How this occurs is not exactly known; it is not necessarily due to the spine, as the same escape into the tissues occurs in spineless eggs, such as those of _Schistosoma japonicum_. The eggs, then, pass as foreign bodies through the tissues. Another hypothesis is that the worms leave the veins in order to lay their eggs, but the evidence is against this. _Caval System._--Occasionally worms that have passed through the vesical plexus may be found in the iliac vein, inferior vena cava, and even the lungs. If the worms are young they contain a lateral-spined egg; if adult, numerous (50 to 100) terminal-spined eggs. _Lungs._--When the liver is strongly infected with (terminal-spined) eggs it is possible that by passive movements some may pass into the intralobular veins, and thence by the inferior vena cava to the lungs. _Gall-bladder._--Similarly terminal-spined eggs pass into the bile-capillaries and gall-bladder (where they may be abundant), and so into the fæces. _Detection of Eggs._--Occasionally eggs may be found in various other parts of the body. They are best detected by macerating pieces of the tissue in question in about 1/4 per cent. hydrochloric acid at 50 to 60°C. (Looss). Pathological changes:-- _Rectum._--These have been studied thoroughly by Letulle in the case of an apparently pure infection of the rectum.[274] They take the form of a chronic diffuse inflammation, which may result in--(1) ulceration, or (2) hyperplasia of the mucosa, producing adenomata. [274] It is noteworthy that in this almost classical case no worms were found in any of the sections. It is further noteworthy that the eggs in the rectum showed great irregularity of form. Eggs with a spine at each end were not uncommon; exceptionally eggs with two polar spines and one lateral. _Ulcerative Form._--The _mucosa_ is transformed into a mass of vascular connective tissue. The connective tissue spaces next become invaded by numerous mononuclear cells. The tissue itself undergoes diffuse sclerosis, becoming hard and fibroid. Eventually ulcerative necrosis sets in. During these changes the Lieberkühn glands are destroyed. The process does not extend to the submucosa, in this respect differing from that in chronic dysentery. _Hyperplastic Form._--The Lieberkühn glands of the mucosa at first hypertrophy; then there is an actual hyperplasia resulting in adenomata. The interstitial tissue of the glands is also greatly hypertrophied, giving rise to very vascular granulations. These growths are often hollow and contain worms. Many eggs are found in the mucosa on their way to the lumen of the gut. The _muscularis mucosa_ is thickened up to twice or even ten times the normal. Its vessels are dilated (36 µ to 80 µ), but they do not allow of the passage of worms. The _submucosa_ is profoundly changed; rigid and hard instead of supple. It is here that the greatest number of eggs occur. A remarkable condition of endophlebitis exists in the veins of the submucosa, not only in the smaller ones but also in the larger ones (370 µ by 270 µ). This endophlebitis results in a more or less complete occlusion of the vessels of the lumen. The _muscular coats_ are free from change, also their veins. The _Serous Coats_.--The veins about 1,900 µ, also show endophlebitis. Besides the rectum, in extreme cases even the transverse colon, the cæcum and small intestine may be affected. _Bladder._--In the early stages the mucosa is deep red and swollen like velvet, or there may be localized patches of hyperæmia or extravasation. The subsequent changes take two chief forms:-- (1) _Sandy Patches._--The mucosa looks as if it were impregnated with a fine brownish or yellowish powder (myriads of ova). This is accompanied by a gradual hypertrophy and new formation of connective tissue, so that dry, hard or plate-like patches with this sandy appearance arise; the thickening eventually affects all the coats of the bladder. In the older patches many of the eggs are calcified. These patches sooner or later break down, ulcerate and necrose. Phosphatic deposits are abundant and stone is common. These patches are not found in the rectum. (2) _Papillomata._--Where the inflammatory change produced by the eggs gives rise to hypertrophy and hyperplasia of the mucosa, papillomata result, the axis of which is formed by connective tissue of the submucosa. These are most variable in shape and form and bleed readily, and sometimes contain cavities of extravasated blood. As in the rectum, it is in the submucosa that eggs are most abundant, and worms in copulâ occur in the veins of this layer, but endophlebitis is not as general as described in the rectum. Malignant disease of the bladder is not an uncommon sequela of bilharziasis. Besides the bladder, the ureters and kidneys may in advanced cases be involved. The prostate and vesiculæ seminales are commonly diseased. Eggs have been recorded in the semen. The urethra is frequently attacked; the vagina in the female. Eggs also occur in the lymphatic glands of the gut. _Geographical Distribution._--East Africa: Nile Valley, Red Sea Coast, Zanzibar, Portuguese East Africa, Delagoa Bay, Natal, Port Elizabeth. South Africa: Cape Colony, Orange Free State, Transvaal, Mauritius, Bourbon, Madagascar. West Africa: Angola, Cameroons, Gold Coast, Gambia, Senegal, Sierra Leone, Lagos, Nigeria. North Africa: Tripoli, Tunis, Algeria, parts of the Sahara. Central Africa: Sudan, various portions. Uganda, Nyasaland. It occurs with varying frequency in these regions. It is probably more widely spread than this list implies, as undoubtedly many cases are seen which are not recorded. Isolated cases have been recorded from Arabia, India,[275] Greece, Cyprus. [275] In a case from Madras, recorded by Stephens and Christophers, the eggs were long and spindle-shaped, quite unlike the eggs of _Schistosoma hæmatobium_. [Illustration: FIG. 174.--_Schistosoma hæmatobium_, Bilh.: genitalia of the female. _V.s._, ventral sucker; _I._, gut cæca; _V.d._, vitelline duct; _V.sc._, vitellarium; _O._, ovary; _Oe._, œsophagus; _Sh._, shell gland; _U._, uterus. Magnified. (After Leuckart.)] The means by which infection is brought about are still uncertain; we only know that the miracidia (fig. 175) enclosed in the discharged eggs do not hatch if the eggs remain in the urine, but after cooling perish. As soon, however, as the urine is diluted with water the shell swells, generally bursting lengthways, and releases the miracidium from its investing membrane, so that it can swim about with the aid of its cilia. In its structure it differs but little from the miracidium of _Fasciola hepatica_, as, for instance, in the lack of eyes; the two large gland cells situated on either side of the intestinal sac are also present in the miracidia of _Fasciola hepatica_. _Sarcode Globules._--This is a term applied to certain globules which at times appear in the miracidium and are later ejected. Some authors consider them as indicative that the miracidium has developed into a sporocyst, but Looss considers them to be degeneration products. The Bilharzia mission, under R. T. Leiper, sent to Egypt by the War Office early in 1915, reports that cercariæ of bilharzia type were recognized in four of the commonest fresh-water molluscs around Cairo. With material obtained from naturally infected _Planorbis boissyi_ acute bilharziosis was experimentally produced in rats, mice, and monkeys. Infection takes place experimentally through the skin and also through the mucous membrane of the mouth and œsophagus. The miracidium, after entering the mollusc, develops into a sporocyst. This gives rise not to rediæ, but to secondary sporocysts, which, in turn, produce cercariæ. These, like the adult worm, differ from other distomes in lacking a muscular pharynx. *Schistosoma mansoni*, Sambon, 1907. According to Manson, Sambon and others, the eggs with lateral spines belong to a species different from _Schistosoma hæmatobium_. Infections with this species only are said to occur in the Congo, Southern States of North America, West Indies (Guadeloupe) and Brazil (Bahia). The following characters, according to Flu, differentiate this species: (1) In the male the transition from the anterior portion of the worm to the lateral fields (the infolded portions which form the gynæcophoric canal) is not a gradual one as in _Schistosoma hæmatobium_, but in this case the lateral fields rise suddenly, almost at right angles to the anterior portion. (2) The ovaries have a well-marked convoluted course as in no other schistosome. (3) The oötype is symmetrical in reference to the long axis of the body, its duct being lateral on the ventral side (Looss’ explanation of this we have already given). (4) The worms live exclusively in portal vein and tract. (As lateral-spined eggs occur also in the bladder, this is not exactly true.) [Illustration: FIG. 175.--Ovum of _Schistosoma hæmatobium_, Bilh., with miracidium, which has turned its anterior end towards the posterior end of the egg. 275/1. (After Looss.)] ------------------------------------------------------------------ |*Schistosoma hæmatobium*, Bilharz, 1852. | | | |Male, four or five large testes. Gut forks unite late, so that the| |single gut stem is short. Female, ovary in posterior half of body.| |Uterus very long, voluminous, with many terminal-spined eggs, some| |lying in pairs. Vitellaria in posterior fourth of body. Cercariæ | |in _Bullinus contortus_ and _Bullinus dybowski_ (syn.: _Physa | |alexandrina_) in Egypt. | | | | | |*Schistosoma mansoni*, Sambon, 1907. | | | |Male, eight small testes. Gut forks unite early, so that the | |single gut stem is very long. Females, ovary in anterior half of | |body. Uterus very short; usually only one lateral-spined egg at a | |time _in utero_. Vitellaria occupy posterior two-thirds of body. | |Cercariæ in _Planorbis boissyi_ in Egypt. | | | |The above morphological descriptions are founded on worms of each | |species, derived from experimentally infected mice (Leiper, R. T.,| |_Brit. Med. Journ._, March 18, 1916, p. 411). | ------------------------------------------------------------------ *Schistosoma japonicum*, Katsurada, 1904. Syn.: _S. cattoi_, Blanchard, 1905. _Male._--Eight to 19 mm., but extreme limits are 5 to 22·5 mm. Consists of a short fore-body, separated by the ventral sucker from the hind-body. The ventral sucker is stalked and somewhat larger than the oral sucker. Both suckers are larger than the corresponding ones in _S. hæmatobium_. Body usually smooth, but in the fresh state numerous fairly evident spines along the margin of the canal. Œsophagus: two bulbs. The junction of the gut forks more posterior than in _S. hæmatobium_, the median united gut stem occupying a quarter to one-fifth to one-sixth of the body length. An excretory canal runs along each side of the body, opening into the dorsal excretory pore. Testes irregularly elliptical, six to eight in number, in the anterior part of hind-body. The vasa efferentia unite into a common vas deferens which opens directly behind the ventral sucker. The seminal vesicle lies just behind this. [Illustration: FIG. 176.--_Schistosoma japonicum_: anterior end with testes; posterior end with point of union of cæca. Length of worm about 10 mm. (After Katsurada.)] _Female._--Up to 26 mm., generally thinner than the male. Surface smooth. Suckers armed with fine spines. Ventral sucker larger than oral. Body thicker behind the region of the ovary. The gut forks unite immediately behind the ovary. The united gut much thicker than in _S. hæmatobium_. Ovary elliptical, almost in the mid-body, its hinder portion dilated. The oviduct arises from its posterior end and then runs sinuously forward, where it is joined by the vitellarian duct; the vitellarium well developed, extending from behind the ovary almost but not quite to the posterior end as in _S. hæmatobium_. Shell gland ducts enter at the junction point of oviduct and vitelline duct. The canal here forms an oötype and then proceeds as the uterus to open directly behind the ventral sucker. The uterus occupies almost half the hind-body. In _S. hæmatobium_ this is not so. The uterine canal is cleft-like, _i.e._, its dorso-ventral diameter is much greater than its lateral diameter. The number of eggs varies from about 50 to 300 from observations made in various hosts. _Eggs._--_In utero_ assume various shapes, as they are soft; the lumen of the uterus is narrow. Outside they are oval, faint yellow, double contoured. In fæces the eggs measure 83·5 µ, by 62·5 µ (man); 85 µ by 61·5 µ (cattle); 98·2 µ by 73·8 µ (dog). The eggs have either small lateral spines or thickenings, and Looss at the opposite side has described cap-like thickenings. The eggs in the tissues undergo various deformities, and may contain a miracidium, as also the eggs in fæces do; or the contents may consist of granular matter or amorphous masses or they may be calcified. Lymphocytes and giant cells may also invade the eggs. [Illustration: FIG. 177.--_Schistosoma japonicum_, male and female in copulâ. × 60. (After Katsurada.)] [Illustration: FIG. 178.--_Schistosoma japonicum_: eggs from human liver, showing “spines” and “hoods” at opposite pole. (After Looss.)] _Mode of Infection._--The miracidia hatch in water in as little as fifteen minutes, but the majority in one to three hours. They will live in water for about twenty-four hours. In water they undergo a transformation into “larvæ,” which then penetrate the skin, as has been shown by Japanese writers to hold good for man, cattle, dog and cat. The penetration of the skin is attended with an eruption on the legs, “Kabure.” The exact route by which the worms reach the portal vein is uncertain. Infection in Japan takes place from spring to autumn, especially May to July, when the soil is contaminated with manure of cattle infected with _S. japonicum_. They also appear to develop in molluscs. Leiper and Atkinson found cercariæ (in sporocysts) in the liver of a mollusc, _Katayama nosophora_. They infected mice by immersing them in water containing liver emulsion and so free cercariæ, thus confirming the similar results of Miyairi and Suzuki. [Illustration: FIG. 179.--_Schistosoma japonicum_: from dog. Uterine egg. × c. 800. (After Katsurada.)] [Illustration: FIG. 180.--_Schistosoma japonicum_: from dog. × c. 800. (After Katsurada.)] [Illustration: FIG. 181.--_Schistosoma japonicum_: from dog. Egg from fæces. × c. 800. (After Katsurada.)] _Habitat._--The worm occurs in Japan, China, and the Philippines. The normal host is man and mammals. Cattle, dog and cat are often found naturally infected. Mice can also be experimentally infected. Their seat of election is the portal vein and its branches, especially the mesenteric veins. They either swim free in the blood or remain fixed by their suckers to the intima of the vessels. They have also been found in the vena cava and right heart of a cat, but not so far in the vesical plexus. Eggs are found in the submucosa and mucosa of the gut, especially the colon, and at times in the serosa and subserosa of the small intestine, where they give rise to new growths. Occasionally eggs are found in the brain. The life of the worms is at least two years. _Pathogenic Effects._--Anæmia through loss of blood due to worms; enlarged spleen, toxic in origin (?); phlebitis, thrombosis, due to portal stasis; the eggs, however, cause the greatest mischief. They are carried by the circulation to various organs where they produce inflammation, granulation tissue, and later connective tissue. _Liver._--The eggs reaching this organ give rise to granulomata and hence enlarged liver, and later, when connective tissue is formed, to contraction. The surface is rough and irregularly granular, “parasitic embolic cirrhosis” of Yamagiwa. [Illustration: FIG. 182.--_Schistosoma japonicum_: section through the gut of a Chinaman showing eggs. × 58. (After Catto.)] _Gut._--The eggs in the mucosa and submucosa cause catarrh and destruction of tissue or new growth. In the small intestine the eggs are mainly in the serosa and subserosa, where they give rise to polypoid or branched growths. _Spleen._--Enlarged, at first due to toxin (?) and later due to portal stasis. Eggs in the spleen are uncommon. _Ascites_ also arises from the portal stasis, and is generally present in advanced cases. Eggs may be found in many other situations: glands (numerous), mesentery, stomach, pancreas, kidney, etc. The bladder remains free. [Illustration: FIG. 183.--_Schistosoma japonicum_: liver showing eggs in the intra- and interlobular connective tissue. × c. 80. (After Katsurada.)] Class III. *CESTODA*, Rud., 1808. Tapeworms have been known from ancient times--at all events, the large species inhabiting the intestines of man--and there has never been a doubt as to their animal nature. The large cysticerci of the domestic animals (occasionally of man also) have been known for an equally long period, but they were generally regarded as growths, or “hydatids,” until almost simultaneously Redi in Italy, and Hartmann and Wepfer in Germany, concluded from their movements and organization that they were of animal nature. From that time the cysticerci have been included amongst the other intestinal worms, and Zeder (1800) established a special class (_Cystici_, Rud., 1808) for the bladder worms. Things remained in this condition until the middle of the last century, when Küchenmeister, by means of successful feeding experiments, demonstrated that the cysticerci were definite stages of development of certain tapeworms. Before Küchenmeister, E. Blanchard, van Beneden, and v. Siebold had held the same opinion in regard to other asexual Cestodes. Since the most remote period another question has again and again occupied the attention of naturalists, the question of the morphological nature--that of the INDIVIDUALITY OF THE TAPEWORM. The ancients, who were well acquainted with the proglottids (_Vermes cucurbitani_) that are frequently evacuated, were of the opinion that the tapeworm originated through the union of these separate proglottids, and this view was maintained until the end of the seventeenth century. In 1683 Tyson discovered the head with the double circlet of hooks in a large tapeworm of the dog; Redi (1684) was also acquainted with the head and the suckers of several Tæniæ. Andry (1700) found the head of _Tænia saginata_, and Bonnet (1777) and Gleichen-Rusworm (1779) found the head of _Dibothriocephalus latus_. Consequently most authors, on the ground of this discovery, considered the tapeworm as a single animal, that maintains its hold in the intestine by means of the head, and likewise feeds itself through it. The fact was recognized that there were longitudinal canals running through the entire length of the worm, and it was thought that these originated in the suckers, and that the entire apparatus was an intestine. As, moreover, the segments form at the neck, and are cast off from the opposite extremity, the tapeworm was also compared with the polyps, which were formerly regarded as independent beings. Steenstrup, in his celebrated work on the alternation of generations (1841), was the first to give another explanation. This has been elaborated still further by van Beneden, v. Siebold and Leuckart, and until a few years ago all authorities adopted his views. According to this view, the tapeworm is composed of numerous individuals, something like a polyp colony, and, in addition to the proglottids--the sexual individuals which are usually present in large numbers--there is ONE individual of different structure, the _scolex_, which not only fastens the entire colony to the intestine, but actually produces this colony from itself, and therefore is present earlier than the proglottids. The scolex is a “nurse,” which, though itself produced by sexual means, increases asexually like a _Scyphistoma_ polyp; the tapeworm chain has therefore been termed a _strobila_. Consequently the development of the tapeworms was explained by an alternation of generations. In support of this opinion it was demonstrated not only that the adult sexual creatures, the proglottids, can separate from the colony and live independently for a time, but that in certain Tæniæ, and especially in many Cestodes of the shark, the proglottids detach themselves long before they have attained their ultimate size, and thus separated continue to develop, grow and finally multiply; the scolex also exhibits a certain independence in so far as, though not, as a rule, capable of a free life, yet it in some cases lives as a free being, partly on the surface of the body of marine fishes and partly in the sea. With the more intimate knowledge of the development of the cysticerci, the independent nature of the scolex was recognized. It is formed by a budding of the bladder that has developed from the oncosphere, in some cases (Cœnurus) in large numbers, in other cases (Echinococcus) only after the parent cyst has developed several daughter cysts. Released from its mother cyst and placed in suitable conditions, it goes on living, and gives rise at its posterior end by budding to the strobila, the proglottids of which eventually become sexual individuals. In order to make this clearer we will briefly summarize what takes place in the jelly-fishes. By _metamorphosis_ is meant a developmental change in the _same_ individual, while alternation of generations, or _metagenesis_, implies a stage in which _reproduction_ of individuals takes place by a process of budding or fission. This _asexual_ reproductive stage _alternates_ with the _sexual_ mode of reproduction. Thus in the development of the Scyphozoa (jelly-fishes) we have:-- (1) The fertilized egg cell divides regularly and forms a _morula_. (2) By accumulation of fluid in the interior this becomes a closed sac with a wall formed of a single layer of cells, forming the _blastosphere_ or _blastula_. (3) One end of the sac is invaginated, forming a _gastrula_. (4) The gastrula pore or mouth closes, forming again a sac, the walls of which have two layers, forming a _planula_. (5) This becomes fixed to a rock, an invagination forms at one end, a depression--the stomodæum--communicating with the enteric cavity. Tentacles grow out and we have a _Scyphozoön polype_, _Scyphistoma_ or _Scyphula_. It is to this stage that Steenstrup gave the name “nurse” (“wet-nurse”), because it nourished or produced asexually the succeeding forms. (6) _Asexual reproduction_ by transverse fission occurs in this, forming a pile of saucer- or pine-cone-like animals which before this time had been considered to be a distinct animal, which was called _strobila_ from its resemblance to a pine-cone. This is the alternate generation. (7) The individuals of the strobila become free and are called _Ephyrulæ_. (8) These develop finally into adult sexual jelly-fish, _Scyphozoa_, so that comparing a tapeworm with this we have (_a_) egg, (_b_) scolex (= Scyphula or “nurse”), (_c_) asexual reproduction of the tapeworm chain (= strobila), (_d_) development of the individuals of the chain (proglottids) into sexual adults. Van Beneden’s terminology for these stages is the following: Ciliated embryo = protoscolex; scyphistoma = deutoscolex (or scolex); free Ephyrula = proglottis. According to this view, as is the case in many endoparasitic Trematodes, asexual reproduction by budding occurs at two stages of the whole cycle of development, _viz._ (1) in the formation of the scolex by budding from the bladder (“nurse”), (2) in the formation of the strobila by budding from the scolex (“nurse”). But in cysticercal larval forms it appears that the scolex does not arise in this way but is simply a part of the proscolex (hexacanth embryo), becoming invaginated into it for protection, so that there is no asexual gemmation here. It has been questioned also whether the strobila also arises by gemmation. If it does, the tapeworm is a _colony_ of zoöids produced by budding from the asexual scolex; if it is not produced in this way, then the tapeworm is to be regarded as an _individual_ in which growth is accompanied by segmentation. Against the “colony” view are the facts that the muscular, nervous, and excretory systems are continuous throughout the worm, and that some tapeworms, such as _Ligula_, are unsegmented. Finally, if the tapeworm is an individual the question arises which is the head end. As new segments are formed at the neck, and as this point in annelids is the antepenultimate segment, the scolex must be the last or posterior segment. The caudal vesicle or bladder of larval forms is consequently anterior. According to this view, in tapeworms as among many endoparasitic flukes, an _asexual_ multiplication occurs at two points of the whole cycle of development, which is as follows: (1) egg, (2) oncosphere or hexacanth embryo, (3) bladder (cysticercus or hydatid), (4) (after digestion of the bladder) by budding, the scolex, (5) by budding from the scolex the sexual proglottids, (6) the egg; (4) and (5) being the two asexual stages. ANATOMY OF THE CESTODA. If we except the tapeworms with only one proglottis, the CESTOIDEA MONOZOA, Lang = _Cestodaria_, Monticelli, we can always distinguish in the Cestodes, in the narrower sense, one scolex or head and a large or small number of segments (proglottids). The SCOLEX serves the entire tapeworm for fastening it to the internal surface of the intestinal wall, and therefore carries at its end various organs which assist in this function, and which are as follows: (i) SUCTORIAL ORGANS, _i.e._, the four suckers (acetabula), which are placed crosswise at the circumference of the thickened end of the scolex; further, the double or quadruple groove-like suckers (bothridia), which are diversely shaped in the various genera and families.[276] (2) FIXATION ORGANS (hooklets)[277] that likewise occur in varying numbers and different positions; they may be in the suckers, or outside them on the apex of the scolex; for instance, in many of the _Tæniidæ_ they appear in a circle around a single protractile organ, the rostellum, or the latter may be rudimentary, and is then replaced by a terminal sucker. (3) PROBOSCIS. One family of the Cestodes, the _Rhynchobothriidæ_, carries four proboscides, moved by their own muscular apparatus, on the scolex, and they are beset with the most diverse hooks. (4) TENTACLE-LIKE formations are only known in one genus (Polypocephalus). [276] They may remain simple, and are then not separated from the remaining muscles of the scolex; or they project as roundish or elongated structures over the scolex, hollow on their free surface, and often divided into numerous areas by muscular transverse ribs. They may also carry accessory suckers on their surface. [277] The various parts of a hooklet are thus named from the point backwards: (1) blade or prong, (2) guard or ventral or posterior root, (3) handle or dorsal or anterior root. The thickened part of the scolex that carries the suckers is usually called the head; the following flat (unsegmented) part connecting it with the proglottids is called the neck, and is sometimes quite small. In a few cases the entire scolex (or head) disappears, and its function is then undertaken by the contiguous portion of the chain of proglottids, which is transformed into a variously shaped PSEUDO-SCOLEX. The proglottids are joined to the scolex in a longitudinal row, and are arranged according to age in such a manner that the oldest proglottis is farthest from the scolex, and the youngest nearest to it. The number of segments varies, according to the species, from only a few to several thousands; they are either quadrangular or rectangular; in the latter case their longitudinal axis falls either longitudinal or transverse to that of the entire chain, according as the segments are longer than broad or broader than long. When the number of segments is very large, the youngest ones are, as a rule, transversely oblong, the middle ones are squarish, and the mature ones longitudinally oblong. The posterior border of the segments, as a rule, carries a longitudinal groove for the reception of the shorter anterior border of the following proglottis. The two lateral borders of the segment are rectilinear, but converge more or less towards the front, or they are bent outwards. In most of the Cestodes the segments, just as the neck, are very flat; in rare cases their transverse diameter is equal to their dorso-ventral diameter. As a rule the segments, singly or several united together, detach themselves from the posterior end, in many cases only after complete maturity is attained, and in others much earlier; they then continue to live near their parent colony, to still call it by that name, in the same intestine and continue their development. Even when evacuated from the intestine the proglottids under favourable circumstances can continue to live and creep about, until sooner or later they perish. The first proglottis formed, and which in a complete tapeworm [_i.e._, sexually complete] is the most posterior, is as a rule smaller and of different shape, it also frequently remains sterile, as likewise happens in the next (younger) segments in a few species; otherwise, however, sooner or later the generative organs develop in all the segments, mostly singly, sometimes in pairs; in the latter case they may be quite distinct from each other or possess some parts in common. The term “mature” is used for a proglottid that has the sexual organs fully developed, while “gravid” is used for one containing eggs. Most of the species combine male and female genitalia in the same segment, only a few are sexually distinct (Diœcocestus). In the hermaphrodite species one male and one female sexual orifice are always present, and, in addition, there may be a second female orifice, the uterine opening; as a rule, however, this is lacking, and in one sub-family, the _Acoleinæ_, to which also the genus Diœcocestus belongs, the other sexual orifice, the opening of the vagina, is also absent. The position of these orifices varies; the cirrus and vagina usually open into a common atrium on one lateral border or on a surface of the segments; the orifice of the uterus may be on the same surface or on the opposite one. The surface on which the uterus opens is termed the VENTRAL SURFACE; if this orifice is absent, one must depend on the ovary, which almost always approaches one of the two surfaces; this surface is then called the ventral. The length of the Cestodes--independently of their age--depends on the number and size of the segments, as well as on their contraction; the smallest species (_Davainea proglottina_) is 0·5 to 1·0 mm. in length; the largest may attain a length of 10 m., and even more. The entire superficial surface of the tapeworms is covered with a fairly resistant and elastic layer, which exhibits several indistinctly limited layers and which is usually called a cuticle, which also covers the suckers, and is reflected inwardly at the sexual orifices. In some species fine hairs appear, either on the entire body or only in the region of the neck, on the external surface. In the cuticle there can be recognized, besides the pores, which no doubt are concerned with nutrition, spaces in which lie the ends of sensory cells. Close under the cuticle lies the external layer of the parenchyma (basal membrane), and below this the circular and longitudinal muscles forming the dermo-muscular coat. The matrix cells of the cuticle occur as in the Trematodes, only on the inner side of the peripheral muscles in the external zone of the parenchyma; they are fusiform cells, forming one or two layers, but are not arranged in the manner of epithelial cells (fig. 184, _Sc.c._). They have fine branching processes which run between the dermal muscles, pass through the basal membrane and penetrate the internal surface of the cuticle with small pistil-like enlargements, expanding on the internal surface of the cuticle into a thin plasma layer. [Illustration: FIG. 184.--Schematic representation of a small part of a transverse section of _Ligula_ sp. _Bs._, basal membrane; _Cu._, cuticle; at its base are the endplates of the subcuticular (epithelial) cells; in the centre a cuticular sense organ, _O.s._; _F.v.s._, vitelline follicle; _Exc._, excretory vessel; _C._, calcareous corpuscle; _L.m._, longitudinal muscles; _M.c._, myoblast; _P.m._, parenchymatous or dorso-ventral muscles; _Pl._, plexus of nerve fibres; _A.m._, circular muscles; _Sc.c._, subcuticular or matrix cell; _T.c._, terminal flame cell. 500/1. (After Blochmann.)] In addition to the above mentioned, there are other cuticular formations occurring on the cuticle of some Cestodes, such as immobile hairs and variously formed hooks, such as are seen principally on the scolex. Their development is only roughly known in a few species; they are usually already present in the larval stage, and of the same arrangement and shape as in the fully developed tapeworms; a matter of importance, because by these structures larvæ can be recognized as being those of a certain species of tapeworm. The CUTICULAR GLANDS in Cestodes are scarce. The PARENCHYMA forms the chief tissue of the entire body, and in all essentials its structure is similar to that of the Trematodes. The same doubt exists here also as to the nature of the parenchyma. Recent authors consider that it consists of highly branched cells, the processes of which ramify in all directions. These cells lie in a non-cellular matrix containing fluid vacuoles. This matrix spreads in between and so breaks the continuity of the epidermal cells. [Illustration: FIG. 185.--Half of a transverse section through a proglottis of _Tænia crassicollis_. Cu., cuticle; _Ex.v._, external excretory vessel, to the right of which there is the smaller internal one; _T._, testicular vesicles; _L.m._, longitudinal muscles (outer and inner); _M.f._, lateral nerve with the two accessory nerves; _Sc.c._, subcuticular matrix cells; _Sm.f._, submedian nerve; _Tr.m._, transverse muscles; _Ut._, the uterus, and the middle of the entire transverse section. 44/1.] In the parenchyma of almost all the Cestodes there are found in adult specimens, as well as in larvæ, light-refracting concentrically striated structures, of a spherical or broad elliptical shape, which, on account of their containing carbonate of lime, are termed CALCAREOUS CORPUSCLES (fig. 184, _C._). Their size, between 3 µ and 30 µ, varies according to the species; their frequency and distribution in the parenchyma also varies, but they are chiefly found in the cortical layer. They are the product of certain parenchymatous cells, in the interior of which they lie like a fat globule in a fat cell, but according to others they are _intercellular_ in origin. The MUSCULAR SYSTEM of the proglottids is composed of--(1) the subcuticular muscles (figs. 184 and 185), as a rule consisting of a single layer of annular muscles; (2) longitudinal muscles; (3) dorso-ventral fibres extending singly from one surface to the other, and at both ends expanding in a brush-like manner, and inserted into the basal membrane, consisting of an outer, more numerous, and an inner, less numerous but more powerful layer (the number of bundles in this layer being in certain cases of specific importance); (4) transverse fibres, the elements of which penetrate to the borders of the segments, thus passing through the longitudinal muscles and reaching the cuticle. In the region of the septa the transverse and dorso-ventral muscles form a kind of plate. The mass of parenchyma bounded by the transverse muscles is termed the MEDULLARY layer, while the mass lying outside them is termed the CORTICAL LAYER. It was known long ago that the myoblasts adhere to the dorso-ventral fibres as thickenings, but it is only recently that large star-shaped cells (fig. 184), separated from but connected with them by processes, have been recognized as the myoblasts of other fibres (Blochmann, Zernecke). Within the scolex the direction and course of the muscular layers change. The SUCKERS are parts of the musculature, locally transformed, with a powerful development of the dorso-ventral muscles, now become radial fibres. The ROSTELLUM of the armed Tæniæ, like the proboscis of the _Rhynchobothriidæ_, also belongs to the same category of organs. [Illustration: FIG. 186.--_Dipylidium caninum_: from the cat. In the upper figure the rostellum is retracted, in the lower protruded, _a_, sucker; _b_, hooks of rostellum; _B_, enlarged hook; _c_, apical aperture on scolex; _d_, longitudinal muscles; _e_, circular muscles. (After Benham.)] In the simplest form, the rostellum, or top of the head (as in _Dipylidium caninum_), appears as a hollow oval sac, the anterior part of which, projecting beyond the upper surface of the head, carries several rows of hooks (fig. 186). The entire internal space of the sac is occupied by an elastic, slightly fibrous mass, while the anterior half of the surface of the rostellum is covered by longitudinal fibres and the posterior half by circular fibres. On contraction of the latter the entire mass is protruded through the apical aperture, the surface of the rostellum becomes more arched, and the position of the hooks is, in consequence, altered. The rostellum of the large-hooked _Tæniidæ_, which inhabit the intestine of man and beasts of prey, is of a far more complicated structure, for, in addition to the somewhat lens-shaped rostellum carrying the hooks on its outer surface, there are secondary muscles grouped in a cup-like manner (fig. 187). Every change in the curvature of the surface of the rostellum induces an alteration in the position of the hooks. In the hookless _Tæniidæ_ the muscular system of the rostellum is altered in a very different manner; in a few forms a typical sucker appears in its place. The NERVOUS SYSTEM commences in the scolex and runs through the neck and the entire series of proglottids. Within the proglottids it consists of a number of longitudinal nerve fibres of which those at each lateral border are usually the largest. In the Tæniæ the lateral nerves are accompanied both dorsally and ventrally by a thinner nerve (accessory nerve) (fig. 185); on each surface, moreover, between the lateral nerve and the median plane, there are two somewhat stronger bundles (sub-median), so that there is a total of ten longitudinal nerve bundles. They lie externally to the transverse muscle plates, and the lateral and accessory bundles lie externally to the principal excretory vessels, and are everywhere connected by numerous anastomoses and secondary anastomoses; one typical ring commissure is usually found at the posterior border of the segments. In the _Bothriocephalidæ_ the distribution of the nerve bundles is different (for instance, two lie in the medullary layer), or they are split up into a larger number of branches. In the scolex the nerve bundles are connected in a very remarkable manner by commissures with that which is generally termed the central part of the entire nervous system. There occurs normally a commissure between the two lateral nerves; at the same level, the dorsal and ventral median nerves are also connected at each surface as well with each other as with the lateral nerves, so that a hexagonal or octagonal figure is formed. The so-called apical nerves pass from this commissural system anteriorly, embrace the secondary muscular system of the rostellum semicircularly, and form an annular commissure (rostellar ring) at the inner part of the rostellum. [Illustration: FIG. 187.--Longitudinal section of the head and neck of _Tænia crassicollis_, showing the lens-shaped muscular rostellum, with two hooks lying in the concentric cup-like mass of muscles. _L.m._, longitudinal muscles of the neck; _L.f._, left lateral nerve; _G._, ganglion; _S.c._, subcuticular layer; _W_{1}_, external, _W_{2}_, internal excretory vessel. 30/1. The peripheral nerves arise from the nerve bundles as well as from the commissures situated in the scolex; some go direct to the muscles, while others form a close plexus of nerves external to the inner longitudinal muscles, which plexus likewise sends out fibres to the muscles, but principally to numerous fusiform sense organs (fig. 184, _Pl._); they lie internal to the subcuticular cells and, piercing the cuticle with their peripheral processes, end as projecting “receptor” hairs. Higher organs of sense are not known. The EXCRETORY APPARATUS of the Cestodes is similar to that of other flat worms. The terminal (flame) cells, which hardly differ in appearance from those of the Trematodes, are distributed throughout the parenchyma, but are more common in the cortical than in the medullary layer (fig. 184, _T.c._). Before opening into a collecting tube, the capillaries run straight, tortuously, or in convolutions, anastomosing frequently with one another or forming a _rete mirabile_. The collecting tubes, which have their own epithelial and cuticular wall, and which also appear to be provided with muscular fibres, occur typically as four canals passing through the entire length of the worm (fig. 189); they lie side by side, two (a wider thin-walled ventral, and a narrower thick-walled dorsal one) in either lateral field; in the head the two vessels on each side unite by means of a loop, at the posterior extremity they open into a short pyriform or fusiform terminal bladder which discharges in the middle of the posterior edge of the original terminal proglottis. [Illustration: FIG. 188.--_Tænia cœnurus_, head and part of neck showing nervous system. Enlarged. (After Niemiec.)] This primitive type (fig. 189) of arrangement of collective tubes is subject to variation in most Cestodes, in the scolex as well as in the segments. Indeed, even the lumen of the four longitudinal tubes does not remain equal, as the dorsal or external tubes are more fully developed and become thicker, whereas the ventral or internal ones remain thin, and in some species quite disappear in the older segments (figs. 185, 187). Moreover, very frequently connections are established between the right and left longitudinal branches, as in the head, where a “frontal anastomosis” develops, which in the _Tæniidæ_ usually takes the form of a ring encircling the rostellum (fig. 190), and in the segments of a transverse anastomosis at each posterior border, especially between the larger branches, and more rarely between the smaller collecting tubes also (fig. 191). The so-called “island” formation is another modification, _i.e._, at any spot a vessel may divide and after a longer or shorter course the two branches reunite, and this may appear in the collecting tubes themselves as well as in their anastomoses. The above-mentioned ring in the frontal commissure of the _Tæniidæ_ is such an island; similar rings also frequently encircle the suckers (fig. 190). In extreme cases (_Triænophorus_, _Ligula_, _Dibothriocephalus_, etc.) this island formation extends to all the collecting tubes and their anastomoses. Instead of two or four longitudinal canals only, connected by transverse anastomoses at the posterior border of the segments, there is an irregular network of vessels, situated in the cortical layer, from which the longitudinal branches, having again subdivided, can only be distinguished at intervals, and even then not in their usual number. [Illustration: FIG. 189.--Young _Acanthobothrium coronatum_, v. Ben., with the excretory vessels outlined. Slightly enlarged. (After Pintner.)] [Illustration: FIG. 190.--Scolex of a cysticercoid from _Arion sp._, with the excretory vessels outlined. (After Pintner.)] The opening of the longitudinal branches at the posterior end requires more accurate investigation; it is true that a single terminal bladder is mentioned as being present in many species, but this is also disputed; when the original end proglottis has been cast off, the longitudinal branches discharge separately. Some species possess the so-called foramina secundaria, which serve as outlets for the collecting tubes; they are generally at the neck, but may be situated on the segments. The contents of the excretory vessels is a clear fluid, the regurgitation of which is prevented by the valves present at the points of origin of the transverse anastomoses. The fluid contains in solution a substance similar to guanine and xanthine. _Genital Organs._--With the exception of one genus (_Diœcocestus_, Fuhrm.), in which the species are sexually differentiated, all the Cestodes are hermaphroditic; the genitalia develop gradually in the segments (never in the scolex), the male organs, as is usual in hermaphroditic animals, forming earlier than the female. The youngest proglottids generally do not exhibit even traces of genitalia: these, as a rule, develop first in the older segments, and the development proceeds onwards from segment to segment. In a few exceptional cases (_Ligula_) the sexual organs are already developed in the larval stage, but are only functional after the entry of the parasite into the final host. [Illustration: FIG. 191.--Proglottis of _Tænia saginata_, Goeze, showing genitalia. _C._, transverse excretory canal; _N._, lateral longitudinal nerve; _W._, longitudinal excretory canal; _T._, testicles scattered throughout the proglottis; _Ut._, opposite the central uterine stem (a closed sac); _Ss._, genital pore leading into the genital sinus; above the cirrus and coiled vas deferens (_V.d._), below the vagina (_Vag._), bearing near its termination a dilatation, the seminal receptacle; _Vsc._, the triangular vitellarium, and above it (_Shg._) the shell gland; leading from this to the uterus is seen the short uterine canal, on either side of this the two lobes of the ovary (_Ov._). 10/1.] With the exception of the end portions of the vagina, cirrus and uterus, all the parts of the genital apparatus lie in the medullary layer, except only the vitellaria, which in many species are in the cortical layer. The male apparatus consists of the testes, of which, as a rule, there are a large number,[278] and which lie dorsal to the median plane (fig. 185, _T._); a vas efferens arises from each testis, unites with contiguous vasa, and finally discharges into the muscular vas deferens that is situated in about the middle of the segment. According to the position of the genital pore, the vas deferens opens on the lateral margin or in the middle line in the front of the segment; it is much convoluted or twisted, and frequently possesses a dilatation termed the vesicula seminalis. It finally enters the cirrus pouch, which is usually elongated; within the cirrus pouch lies the protrusible cirrus, which is not uncommonly provided with hooklets. [278] There are, however, tapeworms with only one, others with only two or three testes in each segment. [Illustration: FIG. 192.--_Dibothriocephalus latus._ Upper figure: female genitalia, ventral view. Lower figure: male genitalia, dorsal view. The central portion only of the proglottis is shown. _a_, cirrus sac; _b_, partly everted cirrus; _c_, genital atrium and pore; _d_, vaginal pore; _e_, uterus; _f_, uterine pore; _g_, vagina; _h_, ovary; _i_, shell gland; _j_, vitelline duct; _k_, lateral nerve; _l_, vitellarium; _n_, vas deferens (muscular portion); _p_, vas deferens; _q_, seminal vesicle; _r_ and _x_, vasa efferentia; _s_, lateral excretory canal; _t_, testicular follicles. (After Benham and Sommer and Landois.)] The male sexual orifice almost always opens with that of the vagina into a genital atrium, the raised border of which rises above the edge of the segment and forms the genital papilla (fig. 191). [Illustration: FIG. 193.--Diagram of genitalia of a Cestode. _g.p._, genital pore; ♀ ♂, male and female ducts opening into genital sinus; _c.s._, cirrus sac; _v.d._, coiled vas deferens (“outer seminal vesicle”); _vag._, vagina; _sem. rec._, seminal receptacle; _sp. d._, spermatic duct; _C.c._, fertilization canal; _vit. d._, vitelline duct; _sh. g._, shell gland; _ut. c._, uterine canal; _ut._, uterus; _Ov._, ovary; _p_, pumping organ. _Cf._ figs. 191 and 233. (Stephens.)] The vagina, like the vas deferens, usually runs inwardly and posteriorly, where it forms a spindle-shaped dilatation (receptaculum seminis); its continuation, the spermatic duct, unites with the oviduct, the common duct of the ovaries (fig. 191). The ovaries, usually two in number, are compound tubular glands in the posterior half of the proglottis, which extend into the medullary layer, but ventral to the median plane. At the origin of the oviduct there is frequently a dilatation provided with circular muscles (suction apparatus), which receives the ovarian cells and propels them forward. After the oviduct has received the spermatic duct the canal proceeds as the fertilization canal, and after a very short course receives the vitelline duct or ducts, and then the numerous ducts of the shell glands (oötype). [Although the nomenclature of these parts varies, we may consider the oviduct as extending from the ovary to the shell gland and as receiving the spermatic duct and then the vitelline duct and the ducts of the shell gland. The short piece into which the shell gland ducts open corresponds to the oötype in the flukes, but in the tapeworms this portion of the canal is seldom dilated. From this point the oviduct is continued as a shorter or longer tube, the uterine canal or true oviduct opening into the uterus proper.--J. W. W. S.] The vitellarium may be single, but often exhibits its primitive duplication more or less distinctly, in which case it is situated at the posterior border of the segments in the medullary layer (fig. 191). The original position of the double organ is, moreover, the same as in the Trematodes, _i.e._, at the sides of the proglottids, and thence eventually extending more or less on both surfaces (figs. 192 and 194); the gland is then distinctly grape-like and the follicles lie mostly in the cortical layer. [Illustration: FIG. 194.--Part of a transverse section through a proglottis of _Dibothriocephalus latus_. _Ct._, cuticle; _C._, cirrus; _Vvs._, vitelline follicles; _L.M._, longitudinal muscles; _T._, testicles; _M._, medullary nerve; _S.c._, subcuticle; _T.m._, transverse muscles; _Ut._, uterus. 20/1.] The egg cell that has been fertilized and supplied with yolk cells receives the shell material at the point of entry of the shell gland ducts, and, as a complete egg, then moves onward to the uterus. In those cases in which the uterus in its further course presents a convoluted canal, and may form a rosette (pseudo-phyllidea), there is an external opening which is usually separate from the genital pore, and lies on the same or the opposite surface. In all other cases, however, the uterus terminates blindly and is represented by a longer or shorter sac lying in the longitudinal axis (fig. 191), but in many forms transversely. With the accumulation of eggs it becomes modified in various ways: (1) it sends out lateral branches (fig. 241), or (2) forms numerous isolated sacs (PARENCHYMAL CAPSULES) containing single eggs or groups of eggs (fig. 217); further, (3) in some cases at the blind end one or more special thick-walled cavities are formed (PARUTERINE ORGANS or UTERINE CAPSULES), in which all or most of the eggs are collected, the uterus then undergoing atrophy. In species in which the uterus lacks an opening, simultaneously with the growth of this organ an atrophy of the male apparatus, at least of the testes and their excretory ducts, takes place; this atrophy also frequently occurs in the female glands, so that the entire mature segments have besides the uterus only traces of the genitalia left. In the _Acoleïnæ_ the vagina is more or less extensively atrophied, and in any case has no external opening. A number of genera are distinguished by the duplication of the genitalia in every segment; the genital apparatus in its entirety, or with the exception of the uterus, is double, or the genital glands and the uterus are single, but the cirrus, vas deferens and vagina are double. On comparing the genitalia of the Trematodes and Cestodes the parts will be found to agree, but the vagina of the Cestodes corresponds with the uterus of the Trematodes, and the uterus of the tapeworms to Laurer’s canal of the Trematodes, which in most of the Cestodes has lost its external orifice. DEVELOPMENT OF THE TAPEWORMS. _Copulation._--As each proglottis possesses its own genital apparatus, and male as well as female organs are present, the following processes may occur: (1) self- or auto-fecundation (without immissio cirri); (2) self- or auto-copulation (with immissio cirri); (3) cross-copulation between proglottids of the same or different chains (of the same species); and (4) cross-copulation in the same proglottis in species with double genital pores. These various modes have actually been observed. In those species which lack the vagina (_Acoleïnæ_) it appears that the cirri, which are always furnished with hooks, are driven into the tissues and for the most part reach the receptaculum seminis. The _eggs_ of all Cestodes are provided with shells, but the shells, like their contents, vary. In genera that possess a uterine pore the mature eggs frequently do not differ from those of the Distomata; they have a brown or yellow shell of oval form provided with an operculum, and contain a number of yolk cells in addition to the fertilized ovarian cell (fig. 128), but in other genera (with a uterine pore) the lid is absent and the egg-shell is very thin, the eggs of these genera resembling those of Cestodes in which the secretion of the vitellarium is a light albumin-like substance that contains only a few granules, and in which the egg-shell is very delicate and without operculum. The eggs of _Tæniidæ_, for example, at first consist of egg-shell (oötype), ovum and yolk cells. The egg-shell is as a rule soft, colourless and frequently deciduous, and the yolk is scanty in amount and contains few granules. The eggs are, moreover, more complicated than this. They enlarge and change their shape and various envelopes are developed around the embryo. The egg-shell proper often disappears, and one or more embryonal envelopes, or protoplasmic layers, arise, so that eventually it is difficult to say whether the whole egg is present, and, if not, what the layers that remain really are. [Illustration: FIG. 195.--Egg of _Diplogonoporus grandis_, showing the morula surrounded by yolk cells and granules. 440/1. (After Kurimoto.)] [Illustration: FIG. 196.--Uterine egg of _Tænia saginata_, G. Uterine shell with filaments; the oncosphere with embryonal shell (embryophore) in the centre. 500/1. (After Leuckart.)] The _embryonal development_ in most species takes place during the stay of the eggs in the uterus; in other species it takes place after the eggs have been deposited and are in water. Separate cells or a layer of cells always separate from the segmentation cells, as well as from the cells of the developing embryo, and form one or more envelopes round the embryo; usually two such envelopes are formed, the inner one of which stands in intimate relationship with the embryo itself and is often erroneously termed the egg-shell, but more correctly the embryonal shell or _embryophore_. In some species it carries long cilia, as in _Dibothriocephalus latus_, by aid of which the young swim about when released from the egg-shell; as a general rule, however, there are no cilia and this envelope is homogeneous, or is composed of numerous rods and is calcified, as in _Tænia_ spp. (fig. 197). The second outer envelope (“yolk envelope”) (fig. 207, 3) lies close within the true (oötype) egg-shell, and remains within it when the embryo hatches out, and in many species, as in _Tænia_ spp., it perishes at the end of the embryonal development with the delicate egg-shell which was formed in the oötype, so that one observes not the entire egg with egg-shell but only the embryo in its embryonal shell, _viz._, the embryophore (fig. 197, _a._). The embryo (the ONCOSPHERE) enclosed within the embryonal shell (embryophore) is of spheroidal or ovoid form (fig. 197, _b._), and is distinguished by the possession of three pairs of spines, a few terminal (flame) cells of the excretory system, and muscles to move the spines. NO FURTHER DEVELOPMENT of the oncosphere takes place, either in the parent organism or in the open; in fact, in all cases in which the oncospheres are already formed within the proglottids they do not become free, but remain in their shell; it is only when the oncospheres are provided with a ciliated embryophore that they leave the egg-shell, and they even cast this ciliated envelope after having swum about in water by its means for a week or so. Sooner or later, however, all the oncospheres leave the host that harbours the parental tapeworm and reach the open, either still enclosed in the uterus of the evacuated proglottids, after the disintegration of which they then become free, or after being deposited as eggs in the intestine of the host; they then leave it with the fæces. In the former case also, the slightest injury to the mature proglottids while still in the intestine suffices to allow a part of the oncospheres in their embryophores to be released and mingled with the fæces. Here they are the generally, but falsely, so-called Tæniæ “eggs.” For, as stated above, the “yolk” envelope and the true shell deposited in the oötype have before this disintegrated. [Illustration: FIG. 197.--_a._, oncosphere, in its radially striated embryophore (erroneously termed egg-shell) of _Tænia africana_. Greatly magnified. (After von Linstow.) _b._, freed oncosphere of _Dipylidium caninum_. (After Grassi and Rovelli.) Both oncospheres show six spines.] In other cases, _e.g._, _Hymenolepis_ spp., the uterine (oötype) shell persists in fæces (fig. 230). In any case the oncospheres must be transmitted into suitable animals to effect their further development; in only very rare cases might an active invasion be possible, as, for instance, takes place with the miracidia of many Trematodes. The entry into an animal is, as a rule, entirely passive, that is to say, the oncospheres are swallowed with the food or water. Many animals are coprophagous and ingest the oncospheres direct with the fæces; others swallow them with water, mud, or food contaminated by such fæces. Infection is easily produced artificially by feeding suitable animals with mature proglottids of certain Cestodes or introducing the oncospheres with the food. As the mature tapeworm frequently finds the conditions suitable for its development in only one species of host, or in species nearly related, and perishes when artificially introduced into other hosts, experiment has taught us that to succeed in cultivating the oncospheres certain species of animals are necessary. Thus we are aware that the oncospheres of _Tænia solium_, which lives in the intestine of man, develop only in the pig, and only quite exceptionally develop into the stage characteristic of all Cestodes--the cysticercus in the wide sense of the word--in a few other mammals. The oncospheres of _T. saginata_ develop further only in the ox; those of _T. marginata_ (of the dog) in the pig, goat, and sheep; those of _T. serrata_ (of the dog) in hares and rabbits; those of _Dipylidium caninum_ (of the dog and cat) in parasitic insects of the dog and cat, etc. It is not unusual that young animals only appear to be capable of infection, while older animals of the same species are not so. Once introduced into a suitable animal, which is only exceptionally the same individual or belongs to the same species as the one which harbours the adult tapeworm, the oncosphere passes into the larval stage common to all Cestodes, but varying in structure according to the species. In the simplest case--as, _e.g._, in _Dibothriocephalus_--such a larva resembles the scolex of the corresponding tapeworm, only that the head, provided with suckers, is retracted within the fore-part of the neck. Such a larval form is known as a _plerocercoid_ (πλήερης, full; κέρκος, tail). They differ from the cysticercoids in being solid larval forms, elongated, tape-like or oval, with the head invaginated. The conditions appear to be similar in _Ligula_, _Schistocephalus_, _Triænophorus_, but here the larvæ are very large, indeed as large in the first-mentioned genera as the tapeworms originating from them, and the sexual organs are already outlined; doubtless, however, this stage is preceded by one that corresponds to the scolex of the genus in question, and which represents the actual larval stage. In such cases the development of the body of the tapeworm from the scolex has already begun within the first or intermediate host; in other cases, except in the single-jointed (monozootic) Cestodes, this only takes place in the definitive host. The direct metamorphosis of the oncosphere into the larval forms termed PLEROCERCOID has hitherto not been investigated, although _Ligula_, _Schistocephalus_ and _Bothriocephalus_ are very common parasites, but many circumstances point to the conclusions arrived at by us and by other observers. In the larval stages of other tapeworms we can always distinguish the scolex and a caudal-like appendage, vesicular in the cysticerci (fig. 200), compact in the cysticercoids (fig. 231). The scolex alone forms the future tapeworm, the variously formed appendage perishing. It has now been proved that the appendage, the caudal vesicle, originates direct from the body of the oncosphere, and therefore is primary, and that the scolex only subsequently forms through proliferation on the surface of this appendage. On account of this origin the scolex is generally regarded as the daughter, and the part usually designated as the appendage as the mother, originating from the oncosphere. Accordingly, two modes of development of the larval stage may be distinguished; in the one case, plerocerci and plerocercoids, the oncosphere changes directly into the scolex, thus forming the body of the tapeworm within the primary host; in the other case, cysticerci and cysticercoids, the scolex only forms secondarily in the transformed body of the oncosphere, which later on perishes, the scolex alone remaining as the originator of the tapeworm colony. We may summarize briefly what has been said regarding these larval forms. We have, firstly, solid larval forms without any bladder. These arise _directly_ from the oncosphere and are of two kinds, plerocercus and plerocercoid. _Plerocercus_ is a solid _globular_ larva with the head invaginated into the posterior portion. _Plerocercoid_ (fig. 208) is a solid _elongated_ larva also with the head invaginated into the posterior portion, which is sometimes very long. Secondly, we have larval forms with bladders from which the scolices arise thus _indirectly_ from the oncosphere. They are of two kinds, cysticercoid and cysticercus. _Cysticercoid._--The bladder is but slightly developed and is usually absorbed again. The anterior portion is, moreover, retracted into the posterior, and in some cases there is a long or a stumpy tail (figs. 220, 231). _Cysticercus_, or true bladder worms. (These may be divided into (1) cysticercus proper, consisting of a bladder and one scolex; (2) cœnurus, a bladder and many scolices; (3) echinococcus, a bladder in which daughter bladders or cysts are developed, and then in these multiple scolices.) [Illustration: FIG. 198.--Diagram of a cysticercoid. _Cf._ figs. 220,