Chapter XVII: Appendix: “Rhizopods in Poliomyelitis acuta.” (11)

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.

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.

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.

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.)

In the case of cysticerci a papilliform invagination forms, projecting into the interior of the bladder (fig. 201). The layer of cells forming the papilla becomes divided into two laminæ, the outer[279] of which forms a kind of investing membrane (receptaculum capitis) for the papilla. The head and suckers are now developed on the walls bounding the axial lumen of the papilla. The papilla eventually evaginates, so that the receptaculum capitis now forms the inner surface of the hollow head, which eventually becomes solid.

[279] _I.e._, regarded from the interior or centre of the invagination.

Our knowledge of the development of cysticerci in the wide sense of the word is limited almost exclusively to that of a few true “bladder worms” (cysticerci); in other cases we know either only the terminal stage, _i.e._, the complete larva, or, exceptionally, one of the intermediate stages, but we are not acquainted with a complete series; the description must therefore be incomplete.

We know from feeding experiments that, after the introduction of mature proglottids or of the fully developed ova of _Tænia crassicollis_ (of the cat) into the stomach of mice, the oncospheres escape from the shell in the middle portion of the small intestine, and a few hours later penetrate into the intestinal wall by means of a boring movement; they have been found in this position twenty-seven to thirty hours after the infection. By means of this migration, for which purpose they employ their spines, they attain the blood-vessels of the intestine; indeed, already nine hours after the infection and later they are found in the blood of the portal vein, and in the course of the second day after infection they are found in the capillaries of the liver, which these larvæ do not leave.

Leuckart, in experimental feeding of rabbits with oncospheres of _Tænia serrata_ (of the dog), found free oncospheres in the stomach of the experimental animal, but not in the intestine: however, he came across them again in the blood of the portal vein. The passage through the blood-vessels to the liver is the normal one for those species of _Tænia_ the eggs of which become larvae in mammals; even in those cases in which the oncospheres develop further in the omentum or in the abdominal cavity (_Cysticercus tenuicollis_, _C. pisiformis_), there are distinct changes observable in the liver that lead one to the conclusion that there has been a secondary migration out of the liver into the abdominal cavity. Indeed, one must not imagine that the young stages of the Cestodes are absolutely passive; once they have invaded an organ they travel actively, and leave distinct traces of their passage.

In other cases the oncospheres leave the liver with the circulation, and are thus distributed further in the body; they may settle and develop in one or more organs or tissues. Many oncospheres may, by travelling through the intestinal wall, penetrate through it and attain the abdominal cavity direct; some, perhaps, pass also into the lymph stream. Where there are no blood and lymphatic vessels in the intestinal wall, as in insects, the oncospheres attain the body cavity or its organs direct; in short, they never remain in the intestinal lumen itself, and only rarely--as in _Hymenolepis murina_ of the rat--do they remain in the intestinal wall.

When the infection has been intense, and the body is crowded with
numerous oncospheres, acute feverish symptoms, are induced, to which
the infected animals usually succumb (“acute cestode tuberculosis”);
while in other cases the alterations in the organs attacked--as the
liver in mice and the brain in sheep--may cause death.

Sooner or later the oncospheres of tapeworms come to rest, and are first transformed into a bladder, which may be round or oval according to the species. The embryonal spines disappear sooner or later, or remain close together or spread over some part of the bladder wall (fig. 200). Their discovery by V. Stein in the bladder worm of the “meal worm” (the larva of a beetle, _Tenebrio molitor_) first led to the conclusion that bladder worms (cysticerci) actually originate from the oncospheres of _Tæniidæ_.

The bladder may remain as a bladder, and then by proliferation the scolex forms on its wall (fig. 202), or it may divide into an anterior so-called “cystic” portion and a solid tail-like appendage of various lengths, on which the embryonal hooks are to be found, and this is particularly the case in those larval forms (cysticercoids), _e.g._, those of _Dipylidium caninum_, that develop in invertebrate animals, such as Arthropoda.

As mentioned above one may regard the scolex as an individual that originates through proliferation of the wall of the parent cyst, mostly singly, but in those cysticerci that are termed cœnurus (fig. 201) many scolices occur, whereas in those called echinococcus the parent cyst originating from the oncosphere of _Tænia echinococcus_ (of the dog) first produces a number of daughter cysts, which in their turn form numerous scolices. Echinococcus-like conditions also occur in cysticercoids, as, for instance, in those peculiar to earthworms; and similar conditions prevail in a larval form known as _Staphylocystis_, found in the wood-louse (_Glomeris_). Thus it happens in these cases that finally _one_ tapeworm egg produces not _one_, but numerous tapeworms, for, under favourable conditions, each scolex can form a tapeworm.

The rudiment of the scolex appears as a hollow bud, the cephalic
invagination usually directed towards the interior of the bladder
cavity; on its invaginated surface arise the four suckers, and the
rostellum with the hook apparatus is formed in its blind end; we
thus get a Tænia head, but with the position of the parts reversed
(fig. 201). In many cysticerci the head rises up from the base of the
cephalic invagination and is then surrounded by the latter. A more
or less elongated piece of neck also develops, and even proglottids
may appear, as in _Cysticercus fasciolaris_ (the larva of _Tænia
crassicollis_ of the cat) of the Muridæ, a process somewhat analogous
to that of Ligula, etc.

The period that elapses from the time of infection till the cysticercus is fully developed varies according to the species; the cysticercus of _Tænia saginata_ requires twenty-eight weeks, that of _T. marginata_ seven to eight weeks, that of _T. solium_ three to four months, and that of _T. echinococcus_ longer still.

With one single exception (_Archigetes_) the larvæ do not become sexually mature in the organ where they have developed; they must enter the terminal host, a matter that is usually purely passive, the carriers of the larvæ or infected parts of them being usually devoured by other animals. In this manner, for instance, the larvæ (_Cysticercus fasciolaris_) found in mice and rats reach the intestine of cats; those of the hare and rabbit (_C. pisiformis_) reach the intestine of dogs; those of the pig (_C. cellulosæ_) are introduced into man; those of insects are swallowed by insectivorous birds; those of crustaceans are ingested by ducks and other water fowl; perhaps, also, the infection of herbivorous mammals is caused by their accidentally swallowing smaller creatures infected by larvæ. Indeed, the researches of Grassi and Rovelli have taught us that such an intermediate host is not always necessary; _Hymenolepis murina_ of rats and mice in its larval stage lives in the intestinal wall of these rodents, and as a larva it passes into the intestinal lumen and develops into a tapeworm in exactly the same way as the larvæ of other species that reach the intestine of the terminal host by means of an intermediate carrier. Probably this curtailed manner of transmission also occurs in many other species. In some cases the larvæ actively quit the body of the intermediate host, as in the case of _Ligula_ and _Schistocephalus_, which travel out of the body cavity of infected fish and reach the water, where they may be observed in hundreds in summer, at all events in some localities. The larval stage of _Calliobothrium_--wrongly termed _Scolex_--has been observed swimming free in the sea, and the scolices of _Rhynchobothrium_, without their mother cysts, have been observed free within the tissues of several marine animals. In any case there is almost always a change of hosts, even in the single-jointed Cestodes, for the larva of _Caryophyllæus_, which lives in fishes of the carp family, is found in limicoline Oligochætes, that of _Gyrocotyle_ (Chimæra) in shell-fish (Mactra), and different conditions can hardly be possible for _Amphilina_. _Archigetes_ alone becomes sexually mature in the larval stage, but the life-history of this creature is not well known, so that it is not impossible that the attainment of sexual maturity as a larva in invertebrates (Oligochætes) is perhaps abnormal, and somewhat analogous to the maturity of some encysted Trematodes.

The METAMORPHOSIS OF THE LARVA into the tapeworm is rarely accomplished in a simple manner; the transformation, however, is not complex in the single-jointed Cestodes, nor in _Ligula_ and _Schistocephalus_; the latter is swallowed by birds (_Mergus_, _Anas_, etc.), produces eggs after only a few days, and very soon quits the intestine of its terminal host. In all other cases it is the scolex only which, by proliferating at its posterior extremity, forms the proglottids, after having invaded as a larva the intestine of a suitable host. The mother cysts, or what corresponds to them, die, are digested, absorbed, or perhaps even eliminated; on the contrary, segments found on the scolex during the larval stage, also in the case of _Cysticercus fasciolaris_, are retained. It is not certain whether the larvæ of _Dibothriocephalus_ lose any part.

The time required by the scolex to complete the entire chain of proglottids does not depend only on the number it has to produce, for _Tænia echinococcus_, which, as a rule, only possesses three or four segments, takes quite as long a time for their growth (eleven to twelve weeks) as _T. solium_ with its numerous segments; _T. cœnurus_ is fully developed in three to four weeks, and the same holds good for _Dibothriocephalus latus_, which possesses many more segments than the above-mentioned Tænia of the dog. In a number of species it has been possible to determine fairly accurately the average daily growth; for instance, in _Dibothriocephalus latus_ the daily growth is 8 cm., in _Tænia saginata_ 7 cm., etc.

The history of the development of the Cestodes demonstrates that persons and beasts harbouring larval tapeworms have become infected by having swallowed the oncospheres of the species of tapeworm to which they belong. In regard to _Hymenolepis murina_ alone, it is known that the introduction of the oncospheres into those species of animals which harbour the adult tapeworm leads to the formation of the latter after the development of a larval stage in the intestinal wall; nevertheless, only young animals (rats) are capable of infection, for a previous infection, or the presence of mature tapeworms in the intestine, appears to produce a kind of immunity.

BIOLOGY.

In their adult stage, the tapeworms inhabit almost exclusively the alimentary canal of vertebrate animals, with but few exceptions the small intestine, and a few species select definite parts of it. A small number of _Rhynchobothriidæ_ of marine fishes live apparently always in the stomach, while in rays and sharks the spiral intestine is their exclusive site. Bothriocephali generally attach themselves with their head on to the appendices of the pylorus of fishes; other species (_Hymenolepis diminuta_) occasionally fix their head in the ductus choledochus, and this is more frequent still in the tapeworms of the rock badger (_Hyrax_), which occasionally penetrate entirely into the biliary ducts. _Stilesia hepatica_, Wolffh., has so far only been found in the bile-ducts of its host (sheep and goat, East Africa).

In the disease of sheep induced by Cestodes, the worms have been observed also in the pancreas. Specimens found in the large intestines were probably being evacuated.

The Cestodes are looked upon as fairly inert creatures, this opinion having been formed by observing their condition in the cold cadavers of warm-blooded animals. Actually, however, they are exceedingly active, and accomplish local movements within the intestine, for they have been found in the ducts communicating with the bowel, or in the stomach, and may even make their way forward into the œsophagus.

They also invade other abdominal organs through abnormal communications, or through any that may be temporarily open between the intestine and such organs; they thus reach the abdominal cavity or the urinary bladder, or they work their way through the peritoneum.

They produce changes in the intestinal mucous membrane at the place of their attachment, the alterations varying in intensity according to the structure of the fixation organs. The mucous membrane is elevated in knob-like areas by the suckers; the epithelial cells become atrophied or may be entirely obliterated. _Dipylidium caninum_ bores into the openings of Lieberkühn’s glands with its rostellum, dilating the lumen to two or three times its normal size, while the suckers remain fixed between the basal parts of the cells. Species with powerful armatures penetrate deeper into the submucosa, and some that are not provided with exceptionally strong armatures, or are even unarmed, may be actually found with the scolex embedded in the muscles of the intestinal walls or even protruding beyond (_Tænia tetragona_, Mol., in fowls, etc.). Other species, again, even cause perforation of the walls of the intestine of their hosts.

It is generally assumed that tapeworms, which almost without exception live in the gut of vertebrates, get their nutriment from the gut contents, which apparently they absorb through the whole body surface (cuticular trophopores). In favour of this view is the existence of fat drops in the proglottids, the identity in colour in certain forms between that of the fresh worm and the gut contents and the passage of certain substances derived from medicines (iron and mercury preparation) into the worms in the gut, etc. Whether the suckers are concerned in the absorption of nutriment and to what extent is still questionable.

THE LENGTH OF LIFE OF THE ADULT TAPEWORM certainly varies; as a rule it appears to last only about a year; in other cases (_Ligula_) it averages only a few days, but we are likewise aware that certain species of Cestodes of man attain an age of several or many years (thirty-five). The natural death of Cestodes often appears to be brought about by alterations in the scolex, such as loss of the hooks, atrophy of the suckers and rostellum, finally the dropping off of the scolex; it is unknown whether a chain of segments deprived of its scolex then perishes or whether it first attains maturity. It has already been mentioned that in a few species the foremost proglottids are transformed into organs of fixation on the normal loss of the scolex.

Abnormalities and malformations are encountered relatively frequently
in the Cestodes--such as abnormally short or long segments;
the so-called triangular tapeworms, which--if belonging to the
_Tæniidæ_--always possess six suckers; often also club-shaped
segments occur between normal ones, or there may be a defect in
one segment or in the centre of a number following one another
(fenestrated segments); bifurcated chains of segments have likewise
been observed, as well as incomplete or complete union of the
proglottids, abnormal increase of the genital pores, reversion of
the genitalia. Besides the above-mentioned increase of the number
of suckers on the scolex (in Tæniæ), there may be a decrease in
the number; in other cases the crown of hooks may be absent, or
abnormally shaped hooks may be formed.

CLASSIFICATION OF THE CESTODA OF MAN.

Order. *Pseudophyllidea*, Carus, 1863.

Scolex without proboscis or rostellum. Head “stalk” absent.

Scolex never with four, generally with two (or one terminal)
bothria.[280] Vitellaria numerous. Uterine opening present. Genitalia
do not atrophy when uterus is developed. In large majority of
proglottids eggs (or, if formed, their contents) are at the same
stage of development.

[280] _Bothridia_ or “_phyllidia_” are _outgrowths_ from the scolex. They are concave and extremely mobile. By some authors the term “_phyllidium_” is used for the outgrowth, and the term “_bothridium_” is restricted to the muscular cup. _Bothria_, on the other hand, are grooves more or less wide, the musculature of which is only slightly developed and is not separated off internally from the parenchyma. _Acetabula_, or suckers in the usual sense, are hemispherical cups, without lips and with musculature separated internally from the parenchyma.

Family. *Dibothriocephalidæ*, Lühe, 1902.

Syn.: _Diphyllobothriidæ_, Lühe, 1910.

Genitalia repeated in each proglottid (polyzootic Cestodes). Ventral
and dorsal surfaces flat. Cirrus unarmed. Cirrus and vagina if
non-marginal open on the same surface as the uterus. Uterus long,
convoluted, often forming a “rosette,” never dilates into a uterine
cavity. Eggs thick shelled, operculated, constantly being formed in
mature proglottids.

Sub-family. *Dibothriocephalinæ*, Lühe, 1899.

Syn.: _Diphyllobothriinæ_, Lühe, 1910.

Segmentation distinct. Scolex unarmed, elongated, sharply separated
(generally by a neck) from the first proglottis. Cirrus and vagina
open ventrally. Genital pores non-alternating. Vas deferens
surrounded by a muscular bulb. Receptaculum seminis large, sharply
separated from the spermatic duct.

Order. *Cyclophyllidea*, v. Beneden.

Four suckers always present. Uterine opening absent. Vitellarium
single. Genitalia atrophy when uterus is fully developed.

Family. *Dipylidiidæ*, Lühe, 1910.

Rostellum if present armed. Suckers unarmed. Uterus breaks up into
egg capsules. Paruterine organs absent.

Family. *Hymenolepididæ*, Railliet and Henry, 1909.

Segment always broader than long. Genitalia single. Longitudinal
muscles in two layers. Genital pores unilateral. Testes one to four.
Uterus persistent, sac-like. Eggs with three shells.

Family. *Davaineidæ*, Fuhrmann, 1907.

Rostellum cushion-shaped. Armed with numerous (sixty to several
thousand) hammer-shaped hooks in two (rarely one) rows.

Sub-family. *Davaineinæ*, Braun, 1900.

Suckers armed. Uterus breaks up into egg capsules. Paruterine organs
absent.

Family. _Tæniidæ_, Ludwig, 1886.

Suckers unarmed. Uterus with median longitudinal stem and lateral
branches. Female genitalia at the hind end of the proglottis. Genital
pore irregularly alternating. Testes numerous in front of female
genitalia. Ovary with two lobes (wings). Vitellarium behind the
ovary. Embryophore radially striated.

THE CESTODES OF MAN.

Most of the species to be mentioned live in man in their adult stage and occupy the small intestine; man is the definite host of these parasites, but is not the specific host for all the species; some of these species, as well as others (of mammals), may occur in man also in the larval stage.

Family. *Dibothriocephalidæ.*

Sub-family. *Dibothriocephalinæ.*

Genus. *Dibothriocephalus*, Lühe, 1899.

Syn.: _Diphyllobothrium_, Cobbold, 1858; _Bothriocephalus_, p. p.
Rud., 1819; _Dibothrius_, p. p. Rud., 1819; _Dibothrium_, p. p.
Dies., 1850.

Scolex egg-shaped; dorsal and ventral bothria elongated, moderately
strong, cutting rather deeply into the head; genitalia single in
each proglottis; papillæ in the vicinity of the genital atrium; the
testes and vitellaria are in the lateral fields, the former in the
medullary layer, the latter in the cortical layer on both surfaces,
and occasionally extending to the median line; the ovary ventral,
the shell gland dorsal. The uterus is in the central field, taking a
zigzag course, and frequently forms a rosette.

*Dibothriocephalus latus*, L., 1748.

Syn.: _Tænia lata_, L., 1748; _Tænia vulgaris_, L., 1748;
_Tænia grisea_, Pallas, 1796; _Tænia membranacea_, Pall., 1781;
_Tænia tenella_, Pall., 1781; _Tænia dentata_, Batsch, 1786;
_Bothriocephalus latus_, Bremser, 1819; _Dibothrium latum_,
Dies., 1850; _Bothriocephalus cristatus_, Davaine, 1874[281];
_Bothriocephalus balticus_, Kchnmstr., 1855; _Bothriocephalus
latissimus_, Bugn., 1886.

[281] Until recently this worm, which was understood to belong to a separate species, was proved on examination by R. Blanchard (“Mai. Par.,” 1896), to be _Dibothriocephalus latus_. Compare also Galli-Valerio, in _Centralbl. f. Bakt., Path. und Infektionskr._, 1900 (1), xxvii, p. 308.

Length 2 to 9 m. or more; colour yellowish-grey; after lying in water the lateral areas become brownish and the uterine rosette brown. The head is almond-shaped, 2 to 3 mm. in length, the dorso-ventral axis is longer than the transverse diameter; the head, therefore, generally lying flat, conceals the suctorial grooves at the borders; these suckers are deep and have sharp edges (fig. 205). The neck varies in length according to the degree of contraction and is very thin; there are 3,000 to 4,200 proglottids and there may be more; their breadth is usually greater than their length, but in the posterior third of the body they are almost square, and the very oldest are not uncommonly longer than they are broad. There are numerous testes situated dorsally in the medullary layer of the lateral fields; the vas deferens (fig. 192) passes dorsally in transverse loops in the central field anteriorly and forms a seminal vesicle before its entry into the large cirrus pouch.

The orifice of the vagina is close behind the orifice of the cirrus; the former passes almost straight along the median line posteriorly, and widens into a receptaculum seminis shortly before its junction with the oviduct; the ovary is bilobed, in shape like the wings of a butterfly, ventrally in the medullary layer; the shell glands lie in the posterior recess of the ovary; the uterus, forming numerous transverse convolutions, passes ventral to the vas deferens forwards. Eggs (fig. 207) large, with brownish shells and small lids, 68 µ to 71 µ by 45 µ; the ovarian cell, which is already, as a rule, in process of segmentation, is surrounded by numerous large yolk cells; the proglottids nearest the posterior extremity are frequently eggless.

The eggs, which are deposited in the intestine and evacuated with the fæces, hatch in water after a fortnight or more; the embryonal integument (embryophore) of the oncosphere is provided with cilia; after bursting open the lid of the egg the oncosphere in its embryophore (fig. 207) reaches the water and swims slowly about; often it slips out of its ciliated embryophore, sinks to the bottom and is capable of a creeping motion; sooner or later it dies in the water. The manner and means of its invasion of an intermediate host are still unknown; yet we are aware that the larval stage (plerocercoid, fig. 208), which resembles the scolex and may reach a length of 30 mm., lives in the intestine, in the intestinal wall, in the liver, spleen, genital glands and muscular system (fig. 209) of various fresh-water fish, the pike (_Esox lucius_), the miller’s thumb (_Lota vulgaris_), the perch (_Perea fluviatilis_), _Salmo umbla_, _Trutta vulgaris_, _Tr. lacustris_, _Thymallis vulgaris_ (grayling), _Coregonus lavaretus_, _C. albula_ (in Europe) and _Onchorhynchus perryi_ (in Japan). The transmission of the plerocercoids from these fish to the dog, cat and man (Braun, Parona, Grassi and Ferrara, Grassi and Rovelli, Ijima, Zschokke, Schroeder) leads to the development of the broad tapeworm, the growth of which is rapid. In my experiments on human beings the average number of proglottids formed per diem averaged thirty-one to thirty-two for five weeks, with a length of 8 to 9 cm. According to Parona the eggs appear twenty-four days after man has been infected. Zschokke found the average growth in the experimental infection of man between 5·2 and 8·2 cm. per diem, and the person experimented upon by Ijima evacuated a piece of a _Dibothriocephalus latus_, 22·5 cm. in length, only twenty-one days after the infection.

The “broad tapeworm” is a frequent parasite of man in some districts, but it also occurs in the domestic dog, and on rare occasions is found in the domestic cat (together with _Dibothriocephalus felis_, Crepl.) and fox. French Switzerland and the Baltic Provinces of Russia are the centres of distribution; from the former districts the distribution radiates to France and Italy (Lombardy, Piedmont); from the Baltic Provinces over Ingermanland to Petrograd, over Finland to Sweden (on the shore of the Gulf of Bothnia), in a southerly direction to Poland, and into the Russian Empire and across it to Roumania, and towards the west along the coast of the Baltic Sea to the North Sea, where, however, its frequency considerably diminishes (Holland, Belgium, and the North of France).

In Turkestan and Japan the “broad tapeworm” is the most frequent parasite of man; it has been reported in Africa from the vicinity of Lake N’gami as well as from Madagascar; cases, in part at least imported, have also come under observation in North America.

In Germany _Dibothriocephalus latus_--apart from the fact that it is undoubtedly imported from Switzerland, Russia or Italy--is particularly frequent in East Prussia amongst the inhabitants of the Courland Lagoon district, on the Baltic; it is, moreover, also found in the Province and even in the City of Königsberg. In West Prussia and Pomerania it is very much scarcer.

It is also found in Munich and in the vicinity of the Lake of Starnberg (Bollinger).

Krabbe found it in 10 per cent. of the sufferers from tapeworms in Denmark; Szydlowski found the ova of this worm in Dorpat in 10 per cent. of the fæces examined; Kruse found the worm in 6 per cent. of _post-mortems_; Kessler, in Petrograd, found the eggs in the fæces in 7·8 per cent.; at _post-mortems_ he found the worms in 1·17 per cent., though Winogradoff only found it in 0·8 per cent. In Moscow, according to Baranovsky, 8·9 per cent. of the fæces examined contained the ova of _Dibothriocephalus_. In the interior and southern provinces of Sweden the worm, according to Lönnberg, is only found sporadically, but, on the other hand, in Angermanland about 10 per cent. of the population is affected; while again in Norbotten the majority of persons are affected, and in Haparanda the entire population (with the exception of infants) harbour this parasite. In Switzerland _D. latus_ is very frequent in close proximity to the lakes of Bieler, Neuchatel, Morat and Geneva (according to Zaeslin 10 to 15 to 20 per cent. of the population are affected); the parasite is less frequent in districts one to four hours removed from these lakes.

Of the fish from Swiss lakes examined by Schor those from Lake Geneva were most commonly infected, and especially _Lota_ sp. and _Perea_ sp.

The frequency and distribution have, nevertheless, decreased perceptibly in places; at the commencement of the eighteenth century the broad tapeworm was very common in Paris, at the present date it only occurs when imported (Blanchard); in Geneva, also, according to Zschokke, it has become rarer (formerly 10 per cent., now only 1 per cent.).

The disturbances produced in man by the presence of broad tapeworms are, as a rule, very trifling; in other cases they produce partly gastric disorders and partly nervous symptoms; in a number of cases, again, they set up severe anæmia, apparently caused by toxins produced by the worms and absorbed by the host. There is no danger of auto-infection, as the larval stage lives only in fishes, not in warm-blooded animals. The case reported by Meschede (ova like those of _Dibothriocephalus latus_ in the brain of a man who had suffered from epilepsy for six years) must be otherwise explained.

Human beings, like other hosts, can only acquire the broad tapeworm by ingesting its plerocercoids with the previously mentioned fresh-water fishes; the opportunity for such infection is afforded the more readily by the fact that not only do the lower classes not pay sufficient attention to the cooking of fish, so that all the larvæ that are present may be killed, but also in certain localities the custom exists of eating some parts of these fishes in a raw condition; even the mere handling of the usually severely infected intermediary hosts may occasionally cause infection. The plerocercoids are as well known as, but differ materially in appearance from, the cysticerci (_Cysticercus cellulosæ_) of pig’s flesh. In Germany the occurrence of the plerocercoids of _Dibothriocephalus latus_ has been confirmed in the pike, miller’s thumb and perch of East Prussia, and more particularly in those taken from the Courland Lagoon.

The life of _D. latus_ is a very long one (six to fourteen years), as is deduced from persons who have left _D. latus_ regions after they have been infected.

According to the experiments of M. Schor, plerocercoids of _D. latus_ placed in slowly warmed water completely lose their movement at 54° to 55° C.; they survive the death of their host for several days; they are killed by low temperatures -3° to +1° C. in two days; strong acids and salt solutions kill them at once, also high temperatures, but all the same at least ten minutes is required in boiling or frying fish in order to kill the plerocercoids with certainty.

*Dibothriocephalus cordatus*, R. Lkt., 1863.

Syn.: _Bothriocephalus cordatus_, R. Lkt.

Length, 80 to 115 cm.; the head is heart-shaped and measures 2 by 2 mm. The suctorial grooves are on the flat surface; the segments commence close behind the head and increase rapidly in breadth. At only 3 cm. behind the head they are already mature; the greatest breadth attained by them averages 7 to 8 mm., the length 3 to 4 mm.; the number of proglottids averages 600; the most posterior ones are usually square. The uterine rosette is generally formed of six to eight lateral loops. The eggs are operculated and measure 75 µ by 50 µ.

_Dibothriocephalus cordatus_ is a common parasite of the seal, the walrus and the dog in Greenland and Iceland, occasionally of man also. No doubt its larva lives in fishes.

The statement that _D. cordatus_ also occurs in Dorpat in human
beings has been proved erroneous (_Zool. Anzeiger_, 1882, v,
p. 46), as also has the report that this worm lives in hares in the
neighbourhood of Berlin, whither it was supposed to have been carried
by Esquimaux dogs (Rosenkranz in _Deutsch. med. Wochenschr._, 1877,
iii, p. 620). The parasite stated by the author to be _D. cordatus_
is _Tænia pectinata_, Goeze, which has been known since 1766.

*Dibothriocephalus parvus*, Stephens, 1908.

Largest gravid segments 5 by 3 mm. Uterus forms a central rosette with four to five loops on each side of median line. In a proglottid measuring 3·5 by 2·25 mm. the genital atrium is situated 0·4 to 0·5 mm. behind the anterior margin and the uterine opening the same distance behind the genital atrium. Calcareous corpuscles absent in the preserved specimens. Eggs operculated, 59·2 µ by 40·7 µ.

Distinguished from _Dibothriocephalus latus_--(1) by the size of gravid segments (the minimum width of gravid segments of _D. latus_ is 10 to 12 mm., so that _D. parvus_ is a much smaller worm); (2) quadrate segments of _D. latus_ measure 6 by 6 mm., those of _D. parvus_ 4 by 4 mm.; (3) by the eggs.

From _D. cordatus_ it is distinguished by--(1) _D. cordatus_ has only fifty immature segments, _D. parvus_ has at least 200, possibly more; (2) mature segments of _D. cordatus_ measure 7 to 8 mm., maximum width of _D. parvus_ is 5 mm.; (3) quadrate segments of _D. cordatus_ measure 5 to 6 mm.; (4) _D. cordatus_ has six to eight uterine loops; (5) _D. cordatus_ measures 75 µ to 80 µ by 50 µ.

_Habitat._--Intestine of man (Syrian, in Tasmania).

Genus. *Diplogonoporus*, Lönnbrg., 1892.

Syn.: _Krabbea_, R. Blanch., 1894.

The scolex is short and has powerful suctorial grooves; no neck; the proglottids are short and broad; there are two sets of genital organs side by side in each segment, which in all essentials resemble the single one of _Dibothriocephalus_.

Parasitic in whales and seals, occasionally in man.

*Diplogonoporus grandis*, R. Blanch., 1894.

Syn.: _Bothriocephalus_ sp., Ijima et Kurimoto, 1894; _Krabbea
grandis_, R. Blanch.

Scolex unknown; chain of proglottids over 10 m. in length, 1·5 mm. broad anteriorly, 25 mm. broad posteriorly. The proglottids are very short (0·45 mm.), but 14 to 16 mm. broad. On either side to the right and left of the worm, along the entire ventral surface, there is a longitudinal groove; these grooves are nearer to each other than to the lateral margin; in them lie the genital pores, and they are in the same sequence as in _Dibothriocephalus_; corresponding to the scanty length (0·45 mm.) of the proglottids, the ovary is only developed transversely; the uterus only makes a few loops. Eggs (fig. 195) thick shelled, brown, 63 µ by 48 µ to 50 µ. This parasite has hitherto been observed twice in Japanese. Similar species are known in Cetacea and seals.

*Sparganum*, Diesing, 1854.

The term _Sparganum_, invented by Diesing, is used as a group name of larval bothriocephalid Cestodes whose development is not sufficiently advanced to enable them to be assigned to any particular genus.

*Sparganum mansoni*, Cobb., 1883.

Syn.: _Ligula mansoni_, Cobbold, 1883; _Bothriocephalus linguloides_,
R. Lkt., 1886; _Bothriocephalus mansoni_, R. Blanch., 1886.

These plerocercoids were discovered in 1882 by P. Manson during the _post-mortem_ on a Chinaman who had died in Amoy, twelve specimens being found beneath the peritoneum and one free in the abdominal cavity. Cobbold described them as _Ligula mansoni_, and Leuckart, who contemporaneously reported a case in Japan, termed them _Bothriocephalus liguloides_. Ijima and Murata reported eight further cases, and Miyake records nine further cases, seven of which are recorded in Japanese literature.

The plerocercoid, which hitherto alone is known to us, attains a length of 30 cm. and a breadth of 3 to 6 to 12 mm. The ribbon-shaped body is wrinkled, the lateral borders are often somewhat thickened, so that the transverse section has the form of a biscuit; the anterior end is usually wider and has the head provided with two weak suctorial grooves, either retracted or protracted.

The parasite makes migrations within the body, and thus may reach the urinary passages; then it is either evacuated with the urine or has to be removed from the urethra; not rarely it causes non-inflammatory tumours on various parts of the skin, which are at times painful and at times vary in size.

Nothing is known of its development and origin.

*Sparganum proliferum*, Ijima, 1905.

Syn.: _Plerocercoides prolifer_, Ijima, 1905; _Sparganum prolifer_,
Verdun, Manson, 1907.

These plerocercoids produce an acne-like condition of the skin. The condition is really one of capsules in great abundance in the subcutaneous tissue and less so in the corium and in the intermuscular connective tissue. The encapsuled worms in the corium feel like embedded rice grains and raise the epidermis, giving rise to an acne-like condition. Many thousands occur scattered over the body; in Ijima’s Japanese case there were over 10,000 in the left thigh. The worms when they first appear in the skin cause itching. The capsules are ovoid, generally about 1 to 2 mm. in diameter, but they may be smaller and also much larger. The larger ones occur in the subcutaneous tissue. The capsules consist of dense tough connective tissue.

Each capsule, as a rule, contains one worm, but as many as seven may occur. The skin of areas that have been long infected is swollen and indurated or adherent, giving a somewhat elephantoid appearance. The subcutaneous tissue is thick and filled with slimy fluid or in other parts sclerosed.

_The Worm._--The chief peculiarity is its irregular shape and its reproduction in the larval stage by forming supernumerary heads, which are supposed to wander about the body.

The simplest forms are thread-like bodies, flat or round, 3 mm. long and 0·3 mm. in diameter, but they may be 12 mm. long by 2·5 mm. broad. The narrow end is the head, which in life invaginates and evaginates, but there is no indication of any suckers, except an inconstant terminal depression. In addition to these simple forms the most complicated and irregular forms occur, due to the formation of buds (heads) at various parts. The detachment and growth of a head account for the presence of more than one worm in a cyst. The irregularity in form is also increased by the presence in the subcuticular tissue of the worm of _reserve food bodies_. These bodies are supposed to be of this nature and are spherical, 100 µ to 300 µ in diameter, but also much elongated.

_Calcareous bodies_ in the Japanese worms were 7·5 µ to 12 µ; in the Florida worms 8·8 µ to 17·6 µ.

_Mode of Infection._--Probably from eating uncooked fish.

_Distribution._--Japan, Florida.

Family. *Dipylidiidæ*, Lühe, 1910.

Genus. *Dipylidium*, R. Lkt., 1863.

Rostellum retractile, with several rings of alternating hooks; the
latter with a disc-like base, having the shape of the thorns of a
rose. Genital pores opposite; genitalia double. Testes very numerous
in the central field; ovary with two lobes; the vitellaria, which are
smaller, behind them; the uterus forms a reticulum, in the network of
which the testicular vesicles lie; later on it breaks up into sacs
enclosing one or several eggs. The eggs have a double shell.

*Dipylidium caninum*, L., 1758.

Syn.: _Tænia canina_, L., 1758, p. p.; _Tænia moniliformis_, Pallas,
1781; _Tænia cucumerina_, Bloch, 1782; _Tænia elliptica_, Batsch,
1786; _Dipylidium cucumerinum_, Lkt., 1863.

This worm measures 15 to 35 cm. in length and 1·5 to 3 mm. in breadth. The scolex is small, rhomboidal, and has a club-shaped rostellum on which there are, in three to four rings, forty-eight to sixty hooks resembling rose thorns, the size of those in the foremost being 11 µ to 15 µ and those in the hindmost ring 6 µ. The neck is very short, the most anterior segments broad and short, the middle as long as they are broad; the mature segments are longer than wide (6 to 7 mm. by 2 to 3 mm.), fairly thick, are frequently of a reddish colour, and when cast off resemble cucumber seeds. The genital pores lie symmetrically at the lateral margins; the roundish egg sacs, arising from the uterine reticulum, contain eight to fifteen eggs embedded in a reddish cement substance (in life). The eggs are globular (43 µ to 50 µ,); the embryonal shell (embryophore) is thin, the oncosphere measures 32 µ to 36 µ. Surrounding the embryophore is an albuminous coating, and outside this the thin vitelline envelope (fig. 218).

_Dipylidium caninum_ is a common intestinal parasite of dogs, in which it grows larger (_Tænia cucumerina_, Bloch) than in cats (_T. elliptica_, Batsch); it has, however, also been found in jackals, as well as in human beings, though in the latter it is of comparatively rare occurrence (twenty-four cases), and almost always affects children, generally of tender age. One-third of all the cases in children were sucklings, about a quarter of all the cases recorded were adults, and these occurred throughout all Europe with the exception of Spain and Italy.

The proglottids, which leave the intestine spontaneously, are recognizable by the naked eye on account of their form and reddish colour, as well as their two genital pores. As a rule, the presence of this parasite sets up no marked symptom in the patient.

The corresponding larval form (cysticercoid) lives in the louse of the dog (_Trichodectes canis_), a fact that was first established by Melnikow and Leuckart; according to Grassi and Rovelli, as well as Sonsino, it also lives in the flea of the dog (_Ctenocephalus canis_) and in the flea of man (_Pulex irritans_), but not in its larva. The adult segments, which also leave the rectum of dogs and cats spontaneously, creep about around the anus and get into the hair, and are thus partly dried and disintegrated. Part of the segments, or the oncospheres released by disintegration, are then taken up by lice and fleas, within which they develop into larvæ (cysticercoids). Dogs and cats are thus infected by their own skin parasites, which they bite and swallow whilst gnawing at their fur. The infection of human beings must occur in an analogous manner, by transmission of the cysticercoids present on the lips or tongue of dogs when the latter lick them, or it may be that the vermin of cats and dogs harbouring cysticercoids are accidentally and directly swallowed by human beings.

Family. *Hymenolepididæ*, Railliet and Henry, 1909.

Genus. *Hymenolepis*,[282] Weinland, 1858.

[282] The genus is by some authors divided into two sub-genera--Hymenolepis, s. str., and Drepanidotænia, Raill.

_Drepanidotænia._--Body, broad lanceolate, testes three, female genitalia antiporal beside the testes. Scolex small, with eight hooks. Neck very short, longitudinal muscle bundles very numerous. No accessory sac opening into genital atrium.

_Hymenolepis._--Narrow, female genitalia ventral to or between testes.