Chapter XIX: Appendix: “Rhizopods in Poliomyelitis acuta.” (13)

The development in cattle often remains stationary at the bladder stage, and they are then called “acephalocysts,” or _Echinococcus cysticus sterilis_. According to Lichtenheld, sterile cysts occur in 80 per cent. of cases in cattle, in 20 per cent. in pigs, and in 7·5 per cent. in sheep. In other cases large numbers of small, hollow BROOD CAPSULES are formed in the germ layer, but are not arranged in any particular order. The order of the layers is just the reverse in them to what it is in the parent cyst, that is to say, they have inside a thin non-laminated cuticle and the parenchymatous layer on their external surface. These, theoretically at least, may be regarded as invaginations of the bladder wall giving rise to a cavity with the cuticle internal and the parenchymatous layer external. If we suppose the orifice to close, we should then get an isolated cavity with cuticle internal and parenchymatous layer external, as in the brood capsule (fig. 252). If we next suppose an evagination of the wall of the brood capsule to occur at one point we should get a hollow process _lined_ with cuticle; at the bottom of this we get the scolex and hooklets formed, and a little higher up the tube the suckers (fig. 252, 4). If this hollow scolex is now pictured as being invaginated we get a hollow scolex _covered_ with cuticle and lined by a parenchymatous layer projecting into the cavity of the brood capsule. The two sides of this hollow scolex now fuse and we get a solid scolex projecting into the cavity. Finally, if we imagine once more the rostellum and suckers invaginated into the posterior part of the scolex we get the condition as frequently found in the brood capsules, _i.e._, a scolex covered with cuticle projecting into the cavity, with the rostellum and suckers invaginated into the posterior portion of the scolex (fig. 252A, 7).

A large hydatid may contain many thousands of brood capsules. Each brood capsule is about as big as a pin’s head, and may contain ten to thirty or more scolices. The delicate wall of the brood capsules may rupture, so that the scolices are now free in the mother cyst. These free scolices and also free brood capsules constitute what is known as “hydatid sand,” which settles at the bottom of a glass when hydatid fluid is poured into it. This form occurs chiefly in domesticated animals and is termed _E. veterinorum_, Rud., or _E. cysticus fertilis_.

In man, and only rarely in cattle, the mother cyst first forms “daughter cysts” (_E. hominis_, Rud. [fig. 255]), which, though smaller than the “mother cyst,” resemble it in the structure of their walls; thus they are covered externally by a laminated cuticle and internally by the parenchymatous layer. They originate:

(1) Between the laminæ of the cuticle of the mother cyst from small, detached portions of the parenchymatous layer; during their growth they bulge inwardly or outwardly and may separate themselves entirely from their parent cyst. In the latter case they lie between the mother cyst and the capsule of connective tissue formed by the host (_E. granulosus_ or _E. hydatidosus exogenus_); when growing inwardly they reach the interior of the mother cyst (_E. hydatidosus endogenus_). Their number is very variable and does not depend on the size of the mother cyst. They are as big as, or bigger than, gooseberries.

(2) According to some authors, endogenous daughter cysts arise also from a _metamorphosis of scolices_ that have separated off from the brood capsule. This takes place in the following way: Fluid accumulates in the interior of the scolex, so that eventually nothing remains except a sac consisting of cuticle lined by parenchyma. The cuticle gradually thickens and several layers form (fig. 257).

(3) _Transformation of Brood Capsules into Daughter Cysts._--This is also held to be possible by various observers. New epithelial layers are deposited between the cuticle which lines the brood capsule and the outer parenchymatous layer. This parenchymatous layer gradually disappears and a new parenchymatous layer forms in the interior from the parenchyma of the scolex or scolices. Although it appears strange that a completely formed scolex with specifically differentiated tissues and organs should retrogress to more primitively organized matter, and again become a proliferating bladder, yet we can hardly doubt that the older observations, regarding such a vesicular metamorphosis, of Bremser (1819), v. Siebold (1837), Naunyn (1862), Rasmusser (1866), Leuckart (1881), Alexinsky (1898), Riemann (1899), Dévé (1901), and Perroncito (1902) are correct.

(4) Further, _a fourth method_ of formation of daughter cysts is described by Naunyn as occurring in sterile hydatids, _i.e._, those containing no brood capsules. In this case a portion of the mother wall of the hydatid gets constricted off.

Figs. _257_ and 257A.--Diagram of transformation of a scolex into a daughter cyst (1 to 3): 1, scolex in brood capsule; 2, liquefaction of scolex; 3, daughter cyst; and (4 to 6) of a brood capsule into a daughter cyst; 4, brood capsule with scolex; 5, deposition of new epithelial layers on the inner layer of the parenchyma; 6, disappearance of outer parenchyma and formation of inner parenchyma from the parenchyma of scolex, which has now disappeared. (_Note._--The scolices are out of proportion to the brood capsules and to the daughter cysts. Stephens.)]

It has also been established that not only daughter cysts transplanted into animals develop further (Lebedeff, Andrejew, Stadnitzky, Alexinsky, Riemann), but that this also holds good if only hydatid _scolices_ from man or animals are transplanted into animals (rabbits). They develop into echinococci and can then give rise to brood capsules and scolices. As Dévé further established, hydatid _scolices_ are not capable of developing in guinea-pigs, while corresponding experiments with rabbits are in the large majority of cases successful where the scolices are introduced subcutaneously or into the pleural or peritoneal cavities. It is only in the case of _daughter cysts_ that further growth is obtained in the case of guinea-pigs. Finally it appears, as has been already stated, that brood capsules can transform themselves into daughter cysts, but according to Dévé only within the mother cyst, not after transplantation. Daughter cysts that have been formed in the mother cyst of man and animals behave themselves just as the mother cyst does, _i.e._, they can remain sterile, or give rise to brood capsules and scolices, or even again to fresh cysts--granddaughter cysts. The mother cyst can also die, so that the daughter cysts then lie in the cavity of the connective tissue capsule. The number of the daughter cysts in either case may attain several thousands.

The echinococcus fluid, which originally is formed from the blood
of the host, is light yellow, with a neutral or slightly acid
reaction; its specific gravity averages 1009 to 1015. It contains
about 1·5 per cent. of inorganic salts, half of which is common salt;
in addition (besides water) it contains sugar, inosite, leucine,
tyrosin, succinic acid (associated with lime or soda) and albumens
which are not coagulated by heat; occasionally also the fluid has
been found to contain hæmatoidin and uric acid salts (in echinococcus
of the kidneys), which doubtless demonstrates that the echinococcus
liquid originates from the host. It has been generally assumed that
echinococcus fluid contains a toxic substance the escape of which
into the body cavity (at operation or by bursting of a hydatid
cyst) produces more or less severe symptoms (fever, peritonitis,
urticaria), so much so that one speaks of hydatid intoxication. The
investigations of Kobert, Joest, etc., have, however, shown the
harmlessness of fresh undecomposed hydatid and cysticercus fluid for
rabbits, mice and guinea-pigs, whether inoculated intraperitoneally,
subcutaneously or intravenously. Contrary data or clinical experience
must accordingly depend on other factors.

According to the researches of Leuckart, the growth of the echinococcus is very slow; four weeks after infection the average size is only 0·25 to 0·35 mm., at the age of eight weeks it is 1 to 2·5 mm., and at this period the formation of the central cavity commences; at the age of five months, and with a size of 15 to 20 mm., the first brood capsules with scolices are formed. The consequence of this gradual increase of size is that the organ attacked can maintain its functions by vicarious hypertrophy, and that many echinococci induce no special symptoms and cannot even be diagnosed, the latter circumstance being due to their hidden position.

The echinococcus cannot be said to be scarce in man, as is shown by the following table for Central Europe:--

--------------------+-------+--------------+------------+----------
Place | | No. of |No. of cases|Percentage
|Period |_post-mortems_| of echino. |
--------------------+-------+--------------+------------+----------
Rostock |1861–83| 1,026 | 25 | 2·43
Greifswald |1862–93| 3,429 | 51 | 1·48
Jena |1866–87| 4,998 | 42 | 0·84
Breslau |1866–76| 5,128 | 39 | 0·761
Berlin |1859–68| 4,770 | 33 | 0·69
Würzburg | -- | 2,280 | 11 | 0·48
Göttingen | -- | 639 | 3 | 0·469
Dresden |1852–62| 1,939 | 7 | 0·36
Münich |1854–87| 14,183 | 35 | 0·25
Vienna | 1860 | 1,229 | 3 | 0·24
Prague | -- | 1,287 | 3 | 0·23
Kiel |1872–87| 3,581 | 7 | 0·19
Zürich, Basle, Berne| -- | 7,982 | 11 | 0·13
Erlangen |1862–73| 1,755 | 2 | 0·11
--------------------+-------+--------------+------------+----------

These, however, are only cases that have become known by _post-mortem_; in addition, there are cases that have been treated medically, of which there are a few statements, at all events relating to the principal districts of Germany. According to Madelung, one case of echinococcus occurs in every 1,056 inhabitants in the town of Rostock, in the district of Rostock one to every 1,283, in Schwerin one to every 5,887, and in Ludwigsort one to every 23,685; according to Peiper, in Upper Pomerania one case occurs to every 3,336, in the district of Greifswald one to every 1,535 inhabitants. The northern districts of Pomerania are more affected than the southern ones.

Accordingly, echinococcus is also considerably more frequent in
cattle in Pomerania. On an average in Germany 10·39 per cent. oxen,
9·83 per cent. sheep, and 6·47 per cent. pigs are infected, whereas
in Upper Pomerania 37·73 per cent. oxen, 27·1 per cent. sheep, and
12·8 per cent. pigs are infected; in Greifswald, indeed, 64·58 per
cent. oxen, 51·02 per cent. sheep, but only 4·93 per cent. pigs are
infected. In accordance with these figures _Tænia echinococcus_ must
be frequent in dogs in Pomerania, especially in Upper Pomerania; on
the other hand, the conjecture that the frequency of echinococcus in
Mecklenburg is explained by the occurrence of _Tænia echinococcus_ in
foxes has not been confirmed, as the fox does not harbour this worm
in Mecklenburg.

Beyond the European continent, echinococcus is frequent in the inhabitants of Iceland, Argentine, Paraguay and Australia. In Iceland, according to Finsen, 1 in every 43 inhabitants is affected with echinococcus; according to Jonassen the proportion is 1 to 63; this is due to the habits of the people of Iceland or, in fact, to the frequency of _Tænia echinococcus_ in dogs, and the prevalence of the hydatid in cattle. In certain districts of Australia it is just as frequent. In Cape Colony, Egypt and Algeria echinococcus is not rare, but it is scarce in America and in Asia, with the exception of the nomadic tribes of Lake Baikal.

Echinococcus attacks persons of every age, though it is rare in children up to 10 years of age and in old people. It occurs most frequently between the ages of 21 and 40 years. According to all statistics it preponderates in women (about two-thirds of the cases). The liver is its favourite seat (57·1 per cent. of the cases); next in order come the lungs (8 per cent.), kidneys (6 per cent.), cranial cavity, genitalia, organs of circulation, spleen (3·8 per cent.), etc. As a rule one organ only is invaded; multiple occurrence may originate from one infection, or eventually from a later infection (?), or it may come to pass that from some cause (through the spontaneous rupture of an echinococcus, or the rupture of one caused by an injury or surgical operation) daughter cysts, brood capsules or scolices escape into the abdominal cavity,[294] where they settle or become transformed and go on growing. In the distribution of this secondary echinococcus the great powers of motility of the free scolices must be taken into account (Sabrazès, Muratet, and Husnot).

[294] In such cases the toxic effects of the echinococcus fluid usually--if not always--manifest themselves. Such effects are manifested by severe symptoms of poisoning being set up, by urticaria, peritonitis, and ascites, and not infrequently they cause a fatal termination.

Human echinococci may also die at various stages of development,
become caseous or calcified, or may be absorbed, the cause for this
being either disease of the hydatid itself or inflammation of its
connective tissue capsule; the discovery of the laminated cuticle,
which has great powers of resistance, or the finding of the hooklets
of the scolices is sufficient to form a conclusion as to the nature
of such formations.

Siebold (1853) was the first to rear _Tænia echinococcus_ in the dog by feeding it with the echinococcus of cattle and especially of sheep. Küchenmeister, van Beneden, Leuckart, Railliet and others obtained similar results, and Thomas, Naunyn, Krabbe and Finsen succeeded in rearing _T. echinococcus_ in dogs from the bladder worms of human beings; these grow comparatively slowly (one to three months[295]) and only during the process of growth develop their hooklets in their definite form (fig. 258). It lies in the nature of things that dogs, whether experimentally or naturally infected, almost always harbour _T. echinococcus_ in large quantities. That cats exceptionally harbour these worms has been already mentioned (Dévé). Finally, Leuckart infected young pigs by feeding them with mature segments.

[295] According to Perroncito the scolices had not formed proglottids nine days after feeding, but the latter were present twenty-four days after feeding, although the formation of eggs had not begun.

*Echinococcus multilocularis* (alveolar colloid).

In addition to the form of echinococcus already described, and which is also frequently termed _Echinococcus unilocularis_, there is a second form which occurs in man as well as in animals, and which is termed _E. multilocularis_, s. _alveolaris_ (alveolar colloid).

It was originally regarded as a tumour; its animal nature was first established by Zeller and R. Virchow. The parasite, which varies in size from that of a fist to a child’s head, presents a collection of numerous cysts, measuring between 0·1 and 3 to 4 mm. to 5 mm. in diameter, which are embedded at first in a soft, connective tissue stroma; the cut surface has therefore a honeycomb appearance. The cysts are surrounded by a pellucid and laminated cuticle, and each according to its size encloses either a small-celled tissue or a cavity lined by a parenchymatous layer; the fluid contained in such a cavity may be transparent, or is rendered opaque by globules of fat, bile-pigment, hæmatoidin and fat crystals. According to some authors all or most of these cysts intercommunicate; others state that this is the case at least as regards the cuticle. The scolices are by no means found in all the cysts, and when present only a few, rarely half, of the cysts contain scolices (one or more); it is supposed that at least some of these scolices are formed in brood capsules, and that the former are capable of undergoing a cystic metamorphosis.

One circumstance is peculiar to the multilocular echinococcus of man, namely, the disintegration that sets in at certain stages; in the centre of the parasite a cavity forms that frequently becomes very large and is filled with a purulent or brownish or brownish-green viscid fluid; in this fluid one finds shreds of the wall of the cavity, calcareous bodies, echinococcus cysts, also scolices and hooklets, as well as fat globules and crystals of hæmatoidin, margarine and cholesterin and concretions of lime. Such ulcerative processes, according to Ostertag, are never present in the multilocular echinococcus of oxen,[296] in which the separate cysts are larger and the connective tissue integument less powerfully developed.

[296] This may perhaps be explained by the fact that the hosts are slaughtered before the parasites have attained the size or other conditions necessary to disintegration.

Hardly anything positive is known with regard to the development of the alveolar echinococcus; its peculiar conformation is attributed by some to enormous infection of oncospheres, by others to the abnormal situation of one oncosphere; a few authors ascribe it to infection of lymphatic vessels, others to infection of the biliary ducts or to peculiarities of the surrounding hepatic tissue; Leuckart ascribes it to a grape-like variety of form which continues budding; a few more recent authors consider multilocular echinococcus to be specifically different from unilocular echinococcus, and therefore also different the species of Tænia arising from them. Melnikow-Raswedenkow is also of this opinion. According to this author the oncospheres infect the lumen of a branch of the portal vein in Glisson’s capsule of the liver and grow into an irregularly shaped formation (chitinous coil), which breaks through the vascular walls and thus forms the alveoli. So far the data coincide well with Leuckart’s opinion of the original grape-like form of the _Echinococcus multilocularis_; according to Melnikow-Raswedenkow the “granular protoplasmic substance” (parenchymatous layer) is not only present in the interior of the loculi but also outside, and, moreover, “ovoid embryos” are supposed to develop in the chitinous coils, which, “thanks to their amœboid movements, reach the lumen of a vessel, where, under favourable circumstances, they begin to develop further,” that is to say, they become “chitinous cysts with fantastic outlines,” or also “single-chambered chitinous cysts”; scolices may develop in both. Dévé, however, considers that these embryos are only prolongations of the protoplasmic layer which secondarily cuticularize.

The multilocular echinococcus, which in man produces a severe disease
and almost always leads to premature death, infects most frequently
the liver, but may also be found primarily in the brain, the spleen
and the suprarenal capsule; from the liver by means of metastasis it
may reach the most various organs, especially those of the abdomen,
but also the lungs, the heart, etc. Up to 1902, 235 cases have been
described and up to 1906, 265, being 70 from Russia, 56 from Bavaria,
32 from Switzerland, 30 from the Austrian Alps, 25 from Würtemberg;
the remaining cases are distributed over Central Germany, Baden,
Alsace, France, Upper Italy, North America. In some the origin is
doubtful; in any case after Russia, the mountainous South of Europe
is the principal region of distribution. As to the domesticated
animals, the same parasite is found principally in the ox (according
to Meyer, in Leipzig, in 7 per cent. of the oxen affected with
echinococcus); it is rarer in the sheep and very scarce in the pig.

It has already been mentioned above that recently the multilocular echinococcus has been stated to be specifically different from hydatid or unilocular echinococcus. To this may be added the fact that Mangold, who fed a young pig with oncospheres of a Tænia reared from the multilocular echinococcus, found two growths in the liver four months later, which he took to be _E. multilocularis_, and consequently one has to assume the existence of two different worms. The chief defender of this view, already put forward by Vogler, Mangold, and Müller, is Possett. He bases his opinions on (1) the more restricted distribution of the multilocular hydatid, the former occurring in districts where only cattle are raised, the latter where sheep-breeding is established; (2) that those engaged in looking after sheep are attacked by multilocular, whereas those looking after cattle are attacked by unilocular hydatid; (3) that among the cases of unilocular hydatid occurring in the distribution areas of multilocular hydatid no transitions between the two forms are observed; (4) on the difference in the hooks both in the hydatid as well as in the Tænia stage; the hooks of _Tænia echinococcus_ are plump, sharply curved, and have a short posterior root process the length of which is to that of the total length as 1 to 4·7, whereas on the contrary the hooks of the alveolar echinococcus are more slender, slightly bent, and have a long posterior root process (1 to 2·5); and (5) on the form of the uterus, which in the alveolar Tænia has the form of a spherically distended sac anteriorly.

SERUM DIAGNOSIS OF ECHINOCOCCUS.

(1) _Precipitin Reaction._--Mix equal parts of hydatid fluid (of the sheep) and serum of patient. Keep at 37° C. The reaction is not decisive as it may be given by normal sera.

(2) _Complement Deviation._--Required: (1) Hydatid fluid of sheep (antigen), (2) guinea-pig complement, (3) patient’s serum, (4) red cells of sheep, (5) hæmolytic serum (of rabbit) against sheep’s red cells, (6) 0·8 per cent. salt solution. Mix the antigen + patient’s serum (heated) + complement + salt solution at 37° C. for one hour. Add red cells of sheep + hæmolytic serum. Allow to stand for half an hour at 37° C. It is imperative to make adequate control observations. An example will indicate the method. Salt solution 1·3 c.c. + patient’s serum (heated) 0·2 c.c. + hydatid fluid 0·4 c.c. + complement 0·1 c.c. of serum diluted to a quarter strength + hæmolytic serum and red cell emulsion 1 c.c. Result: no hæmolysis, _i.e._, the patient’s serum contains specific (echinococcus) antibodies.

C. *NEMATHELMINTHES*.

BY

J. W. W. STEPHENS, M.D., B.C., D.P.H.

Bilaterally symmetrical animals, without limbs and with a body
cavity in which the gut or other organs float. They are generally
cylindrical.

Class. *NEMATODA.*

Nemathelminthes with an alimentary canal.

Nematodes are as a rule elongated round worms of a filiform or
fusiform shape; their length varies according to the species from
about 1 mm. to 40 to 80 cm. The outer surface of the body is
smooth or annulated, and at certain points provided with papillæ,
occasionally also with bristles and alar appendages. The anterior end
carrying the oral aperture is usually rather slender, occasionally
quite thin; the posterior end is pointed or rounded; the anus, as a
rule, lies somewhat in front of the posterior extremity. The sexes
are almost always separate, and the male can as a rule be easily
distinguished from the female because the former is smaller and
more slender, its posterior extremity is often spiral or incurved,
or carries an alar appendage, whereas the female is larger and
thicker, and its posterior extremity is straight. In the male the
genitalia open into the anus; the sexual orifice of the female opens
ventrally along the median line in the anterior half of the body,
in the middle, or a little further back. Both sexes, moreover, have
an orifice, the excretory pore, which is situated ventrally in the
median line and about the level of the œsophageal nerve ring.

In large species, even with the naked eye, two lighter transparent
bands--the lateral lines--may be distinguished; they run along the
sides of the body from the anterior to the posterior end, while two
other bands, the median lines, running along the ventral and dorsal
mid-lines, are less evident; in exceptional cases there are also four
sub-median lines. These bands or lines are inward projections of the
ectoderm, and in them lie the nerves and excretory vessels (fig. 260).

Some Nematodes live free in fresh or salt water, in soil, mud or
decaying vegetable matter, others parasitically in the most various
organs of animals, frequently also in plants.

ANATOMY OF THE NEMATODES.

All the Nematodes are covered by (1) a CUTICLE, which in the small species is thin and delicate, while in the larger species it is thickened, and may consist of several layers of complicated structure. Canalicular pores do not occur. According to general opinion, which is confirmed by the history of development, the cuticle is a product of (2) the EPITHELIUM or ectoderm that had formerly existed or is still found beneath it; in young specimens and small species it is perceptible, but in older worms it frequently alters so considerably that not only do the borders of the cells disappear,[297] but a fine fibrous differentiation appears in their cytoplasm. The matrix or ectoderm then has the appearance of an ectodermal syncytium permeated by fibres and strewn with nuclei, so that it is hardly distinguishable from the tissue of (3) the CUTIS, which is always present, though developed to a varying degree. Both layers, matrix and cutis, project internally as ridges and form the lateral lines, while the less marked median lines are produced apparently only by the ectoderm (fig. 260).

[297] In the _Ascaridæ_ isolated epidermal cells grow to a considerable size, and have to do with the sensory apparatus of the lips (Goldschmidt).

Unicellular cutaneous glands are known in parasitic as well as in free-living species; they vary in number and arrangement, and are found discharging some at the anterior extremity and others in the vicinity of the genital orifices. In other cases large numbers of them are present along the lateral lines; they are strongly developed in most of the _Trichotrachelidæ_, where they discharge either along a part of the ventral surface or along the lateral and median lines; they are placed so closely together that the ridges of the cuticle perforated by the orifices have long been known, and have been described, as “rodlet borders,” or “fields of rods.”

As the cutis is immediately adjacent to (4) the DERMO-MUSCULAR TUBE the simple layer of the muscular cells is divided into four quadrants by the longitudinal lines--two dorsal and two ventral (fig. 260). The MUSCLES are in the simplest cases large rhomboid cells that lie two by two in each quadrant, so that on transverse section of the entire worm only eight cells are perceptible. The outer border of the cells is converted into contractile fibrils, while the contiguous inner portion has remained protoplasmic, and contains the nucleus. In large species the muscular cells do not only increase in length (up to 3 mm.) and in number in every quadrant, but their contractile portion curves up to form a groove (like that of a dead leaf) thereby even becoming thicker; simultaneously space is gained for more cells, the protoplasmic parts of these cells (on transverse section) project out of the grooves like vesicles. In all cases there is only one layer of longitudinal muscular cells, which, by contracting, can shorten the body or, by contracting one side, can bend it. In the latter case the muscles of the opposite side have an antagonistic effect, or when all the muscles are contracted, the elasticity of the cuticle acts in the same way. Special muscles exist at the beginning of the gut and at sections of the genital apparatus.

The existence of a cavity between the body and the gut wall has hitherto been generally assumed, and has been referred to the cleavage cavity, and consequently designated as a primary body cavity. More recent investigators, however, state that such a cavity does not exist, but that the space between the longitudinal muscles or their protoplasmic portions and the gut epithelium is filled by a complicated “isolation tissue.” This in the main proceeds from a large cell (_Is._, fig. 262) which lies directly behind the nerve ring dorsal to the œsophagus, and consists of a system of lamellæ which sheathe the muscles and penetrate through them to the cutis and also cover the gut in a thin layer.

We may now consider the “tuft-like” or “phagocytic” organs, which attain 1 cm. in size, and consist of four, six, or even more ramified cells, which lie close to the walls of the body (fig. 261). They are found either only in the anterior part of the body (Ascaris), or throughout the whole length of the body (Strongylus, syn., Sclerostomum), and their position usually corresponds to the lateral lines. In some species there are small protoplasmic cells on the processes of these organs. In consequence of their size they can be recognized with the naked eye, especially when they are loaded with granules of stain (carmine, Indian ink) injected into the body cavity.

INTESTINAL CANAL.--The oral aperture, which is situated at the tip of the anterior extremity, is frequently surrounded by thick lips, or small bristles, or papillæ; it leads to a more or less strongly developed buccal cavity, which is lined by a continuation of the body cuticle, and which in some species is provided with “teeth,” representing differentiated portions of the cuticle.

THE ŒSOPHAGUS (fig. 262), which arises from the base of the oral cavity, is as a rule a short, bottle-shaped tube with triradiate lumen; its wall is chiefly composed of radiating muscular fibres, which give it the appearance of being transversely striped when viewed from the surface. There exist also in its wall three large gland cells (œsophageal glands) and nerves arising from the lateral lines and running forward. The radial fibres cause a dilatation of the lumen, and exercise an effect antagonistic to the elasticity of the cuticle lining the inner surface. The latter has its own particular layer, which is not in direct connection with that of the oral cavity. Special dilator muscles, arising from the dermo-muscular tube and situated at the commencement of the œsophagus, are only known in a few species. The posterior end of the œsophagus presents a bulb-like dilatation, and is frequently provided with small chitinous movable valves. In a few forms, which belong to the _Trichotrachelidæ_ (Trichocephalus, Trichinella), the œsophagus is a very long cuticular tube, beset on its dorsal surface with a series of large nucleated cells. In others (Cucullanus, Ascaris, etc.), a tube, the so-called glandular stomach, lined only by epithelial cells, follows behind the muscular œsophagus. This glandular stomach is, from its structure, easily distinguished from the mid-gut, or chyle intestine, which is likewise cellular. The so-called mid-gut is a tube lined by flat, cubical, or cylindrical cells (fig. 260) surrounded by “isolation tissue”; its transverse section is circular or flattened dorso-ventrally; the lumen may run in a straight line, or it runs a sinuous course through the alternating prominences of the then flat epithelial cells.

The ectodermal hind gut is, as a rule, very short. At the anal opening the cuticle and the subcuticular layers are reflected inwards, forming the lining of the hind gut. In large species the subcuticular tissue forms large cells on which anteriorly lie in addition large “glandular cells.”[298] In the male the ejaculatory duct opens at this point. Around the end part of the gut, either on the chyle intestine or at the beginning of the end gut, there exists a sphincter muscle arising from a muscle cell which acts antagonistically to the two diaphragm-like dilator muscle cells which stretch from the gut to the body wall. In many species large stretches of the gut are provided with dilator muscles. There is sometimes a retrogressive absorption of the gut in the adult stage of a few parasitic species.

[298] In Ankylostomes according to Looss these cells have no glandular function, but are ligaments.

INTESTINAL CÆCA and ŒSOPHAGEAL GLANDS sometimes exist as intestinal appendages; the former are tubular appendages of various size, running backwards or forwards, and arising from the posterior extremity of the œsophagus. They are lacking in many species. The œsophageal glands are unicellular; a dorsal and two subventral glands may be distinguished according to their position; as a rule they open into the œsophagus at a distance from one another. The body of the gland lies in the bulb of the œsophagus, or in the dorsal _cul-de-sac_ arising from it.

THE NERVOUS SYSTEM is sufficiently known in a few species only; it consists of a ring containing fifty to sixty fibres closely surrounding the œsophagus, various groups of ganglion cells, and a certain number of nerves extending anteriorly as well as posteriorly. The remarkably small number of fibres, as well as ganglion cells, is characteristic of the nervous system of all Nematodes. Immediately behind the œsophageal ring (fig. 263, _Lg._) an agglomeration of ganglion cells lies at either side (lateral ganglia); part of their off-shoots form the œsophageal ring, and part are directed posteriorly and ventrally, and unite partly in front of and partly at the back of the excretory pore, with fibres originating direct from the œsophageal ring, and passing along the ventral median line to the back; these fibres then together form the ventral median nerve (fig. 263, _V.m.n._). This nerve, originally consisting of thirty to fifty fibres, becomes in the female attenuated quite evenly in its further course. There is also an agglomeration of ganglion cells close in front of the anus (anal ganglia), and then the median nerve divides in order to combine with the lateral nerves on either side. In the male the median nerve enlarges to nearly the original number of fibres in front of the anal ganglion, which contains seven cells; there is also an anal ring embracing the terminal gut, and there are two ganglion cells in it on each side. In the dorsal median line the dorsal median nerve is alike in both sexes; arising in front with a single root from the œsophageal ring, it gathers its fibres from the lateral ganglia; in the anterior part of the body it consists of thirteen to twenty fibres; in the posterior part of the body the fibres are reduced to four or six; behind the anus it divides and combines with the lateral nerves; the latter consists of two fascicles at either side right up to their most posterior extent--one dorsal and one ventral--which in the greater part of the body do not run in, but beside the lateral lines, and exhibit a different origin anteriorly. The ventral fascicle at each side branches off from the ventral median nerve in front of the excretory pore, whereas the dorsal fascicles originate from the œsophageal ring close to the lateral ganglia. Each of the four fascicles contains only two or three fibres, which run backwards parallel to the lateral lines; a few centimetres in front of the caudal extremity they enter the lateral lines and remain separate from one another up to the level of the anal ganglion; here they amalgamate on either side, after each interpolating one ganglion cell, with the single short lateral nerve which first takes up the forked ends of the ventral and then of the dorsal median nerve; finally, both lateral nerves unite with each other at the back in an arch-like manner.

In the male each ventral part of the lateral nerves becomes thickened by taking up fibres from the ventral nerves, which become thickened posteriorly to the nervus bursalis, which towards the middle gives off a mass of fibres to the “genital papillæ” situated in front of and behind the anus; the number of these fibres averages eighty to 100; in its further course the bursal nerve resembles the corresponding ventral part of the lateral nerves of the female.

The ventral and dorsal nerves are connected by a number of semicircular commissures, which originate from the ventral nerves and serve to supply the dorsal nerve, which is always being decreased by fibres departing from it. It is remarkable that these commissures are not placed symmetrically, and their position also is different in the two sexes; in the female there are thirty-one on the right side and only thirteen on the left side. In the male there are thirty-three commissures on the right side and fourteen on the left, which run into the subcuticular layer, generally in pairs, and usually cross at the level of the lateral lines.

The fibres of the two median nerves are chiefly motor; fascicular processes run from each protoplasmic part of the muscular cells to the median nerves; from these they take up bundles of primitive fibrils, which separate, pass through the protoplasmic part and enter the contractile part (fig. 260). One part of the fibrils, however, penetrates beyond the muscles into the subcuticular layer, where they form a network, probably of a sensory nature, with contiguous fibrils. Nerves directed anteriorly finally originate from the œsophageal ring; they consist each of three fibres, carry three ganglion cells at their point of origin, and enter the sensory organs of the three papillæ surrounding the oral aperture. Two of these little trunks lie in the lateral lines, the remaining four are situated in the middle of the four quadrants (Nn. sub-mediani anteriores).

Parasitic species lack higher ORGANS OF SENSE; free-living worms occasionally have two rust-red eyes, sometimes with lenses, at the anterior part of the body. In addition to the above-mentioned sensory papillæ surrounding the oral aperture and the genital papillæ of the male at the end of the body, another pair exist in the vicinity of the lateral ganglia, the “cervical papillæ,” and two dorsal papillæ in the central region of the body and two lateral ones near the tip of the tail (_Ascaridæ_). The differences in the distribution and number of the sensory papillæ serve for characterizing the larger and smaller groups of Nematodes.

THE EXCRETORY ORGANS of the Nematodes are variable. In a great many cases the apparatus is symmetrical, and consists of a vessel commencing in the posterior extremity in each lateral line (fig. 260), and passing anteriorly. In the vicinity of the anterior extremity both tubes pass out of the lateral lines, bend ventrally, and, in the median ventral line, unite into a short vesicle formed by an ectodermal cell--the cavity of which is lined by a continuation of the cuticle of the body--which opens into the excretory pore (fig. 263, _Exp._). Asymmetry is occasioned through the excretory duct proceeding from the ventral pore to the lateral line, and it here proceeds as (or takes up) the left excretory canal, which anteriorly is a broader tube and runs along the left lateral line; shortly before its union with the excretory duct it throws out a branch to the right towards the lateral line, which, however, always remains weak, and runs posteriorly in the right lateral line; a few smaller branches in addition spring from the left main stem. In other species the right branch is completely suppressed; the entire organ thus lies in the left lateral line, and consists of the excretory duct, which occasionally opens quite in front near the lips, as well as the excretory canal, which throws out a number of lateral branches.

This excretory vesicle is a single elongated or horse-shoe-shaped cell, with a large nucleus and an intracellular tubular system, which is connected with the excretory duct arising from the excretory pore on the outer surface (fig. 326). The so-called ventral gland is the only excretory organ of marine Nematodes, and probably represents a primitive form. Goldschmidt, who has investigated the excretory apparatus of _Ascaris lumbricoides_, considers that the vessels running in the lateral lines are only ducts to which belong a glandular system hitherto overlooked or otherwise interpreted. This system also lies in the lateral lines, and takes the form of two glandular tracts, forming a syncytial tissue in which lie the ducts, one dorsal, one ventral. In parts these tracts are connected by commissures, although their junction with the excretory vessels cannot be clearly made out. These statements, however, require confirmation. The author has further found that the anterior ends of the lateral canals, directly before they bend ventrally, anastomose with one another and give off anteriorly a small blind process, which can be interpreted as a rudiment of a canal coming from the head end, and as a matter of fact, according to Golowin, such anterior excretory canals exist in a number of genera.

In a number of Nematodes (Cheiracanthus, Capillaria, Trichocephalus, Trichinella, etc.), however, special excretory organs are lacking; possibly the cutaneous glands, which are in these species generally powerfully developed, replace these organs.

SEXUAL ORGANS.--With the exception of a few species, the Nematodes are sexually differentiated.

(_a_) _Female Sexual Organs._--The sexual orifice (vulva), surrounded by thick labia, is, as a rule, ventral and varies in position from near the head to near the anus. It leads into a short or long vagina (ectodermic), bifurcating into the two uteri, which may be long or short; the long filiform ovaries are continuations of them (fig. 264). Further there is often, _e.g._, in Ankylostoma, a differentiation into the following parts: (1) _Ovejector_: the specialized portion of the uterus before it joins the vagina; there may be a separate one for each uterus, or a common one for both uteri. (2) _Seminal receptacle_: at the other extremity of the uterus. (3) _Oviduct_: a narrow tube connecting the ovary with the uterus proper. (For the explanation of the terms _convergent_ and _divergent_ uteri _vide_ footnote p. 432.) Uterus and ovaries, which arise in the first place from a single cell, lie between the body wall and the gut and are surrounded by connective tissue. In some species (for instance, Trichinella) the ovary is single.

At the blind end of the ovary there is a mass of protoplasm with
numerous nuclei that multiply continuously. Gradually the nuclei
arrange themselves in longitudinal rows (fig. 265) and the protoplasm
commences to leave the periphery and surround each nucleus. The
nearer to the uterus the more progressive is this loosening process,
until club-shaped cells each containing a nucleus are developed. The
most pointed end of each, however, is still attached to an axial
fibre of protoplasm, the _rhachis_; probably this has some connection
with the nutrition of the ova. Finally the ova fall off and reach the
uterus, where they are fertilized and enclosed in shells.

(_b_) _Male Sexual Organs._--There is never more than one testis (fig. 266), which is a straight or sinuous tube of the same construction as an ovary, and in which the mother cells originate in the same manner as the ova. In the same way as the ovary passes into the uterus, so does the testis pass into the spermatic duct; the latter is often divided into the somewhat dilated seminal vesicle and into the muscular ductus ejaculatorius, which, running ventral to the intestine backward (fig. 267), finally opens into the cloaca. In many species, _e.g._, _A. duodenale_, the ejaculatory duct is surrounded for a greater or less portion of its extent by the cement gland, the secretion of which (brownish or blackish in colour) serves for copulation. The ejaculatory duct of the large _Ascaridæ_ is for the most of its course surrounded by a muscular network which takes its origin from the two dilator cells of the gut (fig. 268 _F_.). The spermatozoa of the Nematodes, it may be noted, only attain their full development after the sperm mother cells have been conveyed by copulation into the uteri of the female genitalia. In their form (sheathless, capable of amœboid motion) they differ from those of most other animals.

SPICULES.--The male genital apparatus is also provided with one or two sacs, situated on the dorsal side of the intestine, and opening into the cloaca. In each sac there is a chitinous rod-like body, the spicule. Further, in many cases there exists, more or less fixed in the dorsal wall of the cloaca, a chitinous structure, the accessory piece or _gubernaculum_, the latter name implying its function of guiding the spicules during copulation (fig. 264A). A special muscular apparatus, consisting of protractors and retractors, moves the spicules. The protractors or exsertors in the large Ascaridæ consist of four flat band-like muscles which surround the spicule sac. Two long muscle cells which arise proportionally far forward on the dorsal side of the lateral line and are inserted into the base of the spicules serve as retractors. The spicules can be projected from the cloacal orifice (anus) during copulation, and when they are introduced into the vagina they serve as prehensile organs, perhaps also as stimulatory organs.

BURSA COPULATRIX.--The males in many genera possess epidermal wing-like appendages at their posterior extremity. These are supported by elongated tactile papillæ called ribs. In the most highly developed bursæ, _e.g._, in the _Strongylidæ_, the ribs are called rays, as they consist not only of nerve fibres but mainly of “pulp,” _i.e._, prolongations of the subcuticular layer. Bursæ are either open, _i.e._, bilaterally symmetrical, or closed, when the posterior border is continuous all round. A _pseudo-bursa_ is one unsupported by ribs or rays, _e.g._, in Trichuris. The bursa serves as an organ of prehension during copulation. Some forms, moreover, carry a sucker at the posterior extremity (_e.g._, Heterakis); in others the spicules and other prehensile organs are absent; they are then replaced by an evertible cloaca, _e.g._, Trichinella.

DEVELOPMENT OF THE NEMATODES.

After impregnation, the ovum develops around itself a delicate membrane (vitelline membrane), and subsequently an egg-shell is formed. This is derived either as a secretion from the uterine wall or it is a further differentiation of the vitelline membrane, the original single membrane splitting into two, the outer becoming the egg-shell. Further the uterus often secretes a special albuminous covering around the egg-shell. The “yolk” granules of the ovum are secretions of the protoplasm of the ovum itself and first appear when the rhachis is formed. In certain cases ova lie in follicles or capsules formed of epithelium cells derived from the ovarian tubes. These cells subsequently fuse and form a membrane--the CHORION.

The shape of the completed eggs is characteristic of the different species, and therefore a single egg often suffices to diagnose the species. According to the species, the eggs may be deposited sooner or later, either before or during segmentation, or with the embryo perfectly developed. Only a few species are viviparous, _e.g._, _Dracunculus mediensis_, _Trichinella spiralis_; in the other Nematodes the further development of the extruded eggs takes place after various lengths of time in the open, in moist earth, or in water. Thick-shelled eggs can maintain their developmental capacity for a long time, even after prolonged desiccation.

Finally, a nematode-like embryo develops, which usually lies somewhat coiled up within the shell, and varies in its further development according to the species to which it belongs.

In the simplest forms, as in the free-living Nematodes, the embryos, apart from their size, resemble their parents, and grow up into these after leaving the egg-shell. In many parasitical Nematodes, however, the young must be called _larvæ_, as they present characters which are subsequently lost.

The manner of conveyance of the eggs or the embryos contained in them after they have left the body into the definite host is very different in the various species.

(1) _Without Intermediate Host._--(_a_) In many the conveyance into the definite host is effected directly after the larvæ have developed within the eggs; thus, for instance, the feeding of suitable animals with the embryo-containing eggs of species of Trichocephalus and Ascaris leads to an infection of the gut, for the young Trichocephali or Ascarides only leave the egg-shell when they have attained the intestine of the final host, in which they become adult.

In other cases (_b_) Ancylostoma, Necator, the larvæ hatch in the open, and live for a time free, changing their form; they grow, cast their skin, and finally gain the intestine of the host by means of water or through the skin, when they lose their larval characters and assume the structure of the adult worm.

(_c_) In a number of Nematodes, however, HETEROGONY occurs. This terms signifies a mode of development in which two structurally different sexual generations of the same species alternate with each other. To these appertains, for instance, _Angiostomum_ (syn.: _Rhabdonema_) _nigrovenosum_, which lives in the lungs of frogs and toads; this Nematode measures about 1 cm. in length and is hermaphrodite (protandric). The eggs are deposited in the pulmonary cavity, and through the cilia of the same reach the oral cavity, where they are swallowed and thus conveyed into the intestine. They pass through the entire gut, and are finally evacuated with the fæces; often, indeed, the young themselves emerge from the egg-shell within the hind-gut of the frogs. These young forms become sexually differentiated, remain much smaller than the parent, their œsophagus is differently constructed (rhabditis form), and they are non-parasitic (fig. 266). After having grown in the open they copulate; the males die soon after copulation, and the females in their own bodies develop a few young, which, given the opportunity to get into frogs, infect them, and are transformed into the hermaphroditic Angiostomum. The same manner of development occurs in other species of the same genus, and also in the case of _Strongyloides stercoralis_.

(2) _With Intermediate Host._--(_a_) Frequently, however, the larvæ of Nematodes make use of one or even two intermediate hosts; their condition then resembles that of Cestodes or Trematodes, excepting that there is never a multiplication within the intermediate hosts. The larvæ become encapsuled amongst the tissues of the intermediate host, and wait till they are introduced with the latter into the final host. For instance, _Ollulanus tricuspis_, the adult form of which is found in cats, previously lives encysted in the muscular system of mice. _Cucullanus elegans_, which attains the adult stage in fishes (perch, etc.), is found encysted in species of Cyclops. Other examples of species that require an intermediate host are _Filaria bancrofti_ and _Dracunculus medinensis_.

Peculiar conditions prevail in the case of (_b_) _Trichinella spiralis_. This species, which in its adult state lives in the intestine of man and of various mammals, is viviparous; the young Trichinæ, however, do not leave the intestine, but reach the intestinal wall (Cerfontaine, Askanazy) in the following way: the female intestinal Trichinæ bore into the intestinal wall, where they are found in the submucosa, or in the lumen of the dilated lacteal vessels. Here the young are born, in the intestinal wall, and leave this position with the lymph stream. Some of them, no doubt, actively bore through the intestinal wall, reaching the lymph or blood-stream, or even pass into the body cavity. What occurs during their further migrations is difficult to say at present. It has hitherto been maintained that the wandering is entirely active; for instance, the ligaturing of an artery would be no protection against the part of the body supplied by such artery being invaded by Trichinella. This observation cannot be otherwise explained than by the active progress of the young Trichinella. The question, however, may be mooted as to where and when the worms quit the blood-vessels, which they for the most part reach through the thoracic duct, the natural connection between the vascular system and the lymphatic system, to wander further independently, and ultimately reach the muscular system, in which they become encysted (fig. 269). Thus the progeny does not leave the body of the host inhabited by the parents, as is generally the case amongst helminthes, but uses it as an intermediate carrier to reach another host, which is then the final host. The latter may belong to another species, or may be another individual of the same species. This second migration is, of course, purely passive.

CLASSIFICATION OF THE NEMATODA.

The Nematodes are usually divided into a number of families, some of
which it is at present impossible to define accurately; moreover, the
definition of many genera is also in an unsatisfactory state.

Family. *Anguillulidæ*, Gervais and van Beneden, 1859.

A “family” name not definable. They comprise a vast number of
small forms, most of which live free in fresh water, in soil, or
in macerating substances; amongst them there are some which live
parasitically on plants, more rarely on animals. They do not exceed
8 mm. in length. The large majority are only 1 to 2 mm., or even
0·5 mm. The uterus is straight. Eggs in the uterus at one time,
one to four. Genera very numerous, but many of them insufficiently
defined (Anguillula, Anguillulina, Rhabditis, Heterodera, etc.).

Family. *Angiostomidæ*, Braun, 1895.

Small Nematodes undefined morphologically, but characterized by
heterogony, _i.e._, there is a free-living “rhabditic” generation
and a parasitic “filariform” generation which succeed one another
(_e.g._, Angiostomum, Strongyloides, Probstmayria).

Family. *Gnathostomidæ.*

Cuticle covered totally or partly with cuticular laminæ fringed
posteriorly with multiple points. Head subglobular, covered with
simple spines. Two spicules. Vulva behind middle of body, parasitic
in vertebrates, especially mammals (_e.g._, Gnathostoma, Tanqua,
Rictularia).

Family. *Dracunculidæ*, Leiper, 1912.

Males very small in proportion to females. Anus absent. Vulva absent
(?). Genera: Dracunculus, Icthyonema (in body cavity of eel and other
fish).

Family. *Filariidæ*, Claus, 1885.

Long thread-like Nematodes. Anus present. Œsophagus without bulb.
Vulva usually in anterior half of body. Two ovaries. Generally
ovoviviparous. Development often requires an intermediate host. This
family is at present ill-defined, but has been already subdivided
into several sub-families, _Filariinæ_, _Onchocercinæ_, _Arduenninæ_.

Family. *Trichinellidæ*, Stiles and Crane, 1910.

Œsophagus consisting of a chain of single cells, the lumen of the
œsophagus passing through their centre. Ovary single. Vulva at
junction of anterior and posterior portions. Sub-families: (1)
_Trichurinæ_, (2) _Trichinellinæ_.

Family. *Dioctophymidæ.*

Body anteriorly armed with spines or unarmed; mouth without lips,
with six, twelve, or eighteen papillæ in one or two circles;
œsophagus very long without a bulb; anus terminal in female; one
ovary; vagina very long; spicule in male very long; bursa cup-shaped
without rays (Dioctophyme, Hystrichis, Eustrongylides).

Family. *Strongylidæ*, Cobbold, 1864.

Bursa, supported by rays, always present. Oviparous.

Family. *Physalopteridæ.*

Mouth with two large lips. Bursa with supporting papillæ in form of a
lanceolate cuticular expansion, with genus Physaloptera.

Family. *Ascaridæ*, Cobbold, 1864.

Rather thick Nematodes. Mouth with three lips--one dorsal, two
latero-ventral. Sub-families: (1) _Ascarinæ_, (2) _Heterakinæ_, etc.

Family. *Oxyuridæ.*

Smallish forms, 4 to 45 mm., with cuticle thickened on each side
for the whole length of body in the form of a lateral flange or
wing. Œsophagus long with a well-marked bulb containing a valvular
apparatus. Tail end of female drawn out into a long point. Eggs
asymmetrical. Males very small (about 2 mm.). One spicule. Genera:
Oxyuris, Passalurus, Ozolaimus, Atractis, etc.