Chapter XVIII: Appendix: “Rhizopods in Poliomyelitis acuta.” (12)

Accessory sac (opening into genital atrium) usually absent. Vas
deferens with an external (outside cirrus sac) and an internal
(inside cirrus sac) “seminal vesicle.” Three testes in each
proglottis. The eggs are round or oval with two to four distinct
envelopes. In mammals and birds.

*Hymenolepis nana*, v. Sieb., 1852.

Syn.: _Tænia nana_, v. Sieb., 1852, _nec_ van Beneden, 1867; _Tænia
ægyptiaca_, Bil., 1852; _Diplacanthus-nanus_, Weinld., 1858; _Tænia_
(_Hymenolepis_) _nana_, Lkt., 1863.

The worm is 10 to 45 mm. in length and 0·5 to 0·7 mm. in breadth; the head is globular, 0·25 to 0·30 mm. in diameter. The rostellum has a single circlet consisting of twenty-four or twenty-eight to thirty hooks, which are only 14 µ to 18 µ in length. The neck is moderately long; the proglottids are very narrow, up to 200 in number, 0·4 to 0·9 mm. in breadth, and 0·014 to 0·030 mm. in length. The eggs are globular or oval, 30 µ to 37 µ to 48 µ; the oncospheres measure 16 µ to 19 µ in diameter, with two coats, separated by an intervening semi-fluid substance (fig. 224).

This species was discovered by Bilharz in Cairo in 1851; it was found by him in great numbers in the intestine of a boy who had died of meningitis. For several years this was the only case, until 1885, since when numerous cases have come to light. Spooner (1873) even reported a case from North America, which may, however, have related to _Hymenolepis diminuta_. In Europe the worm is particularly frequent in Sicily, but it has also been repeatedly observed in North Italy; it has, moreover, been reported from Russia, Servia, England, France, Germany, North and South America, the Philippines, Siam and Japan, in all over 100 cases. Notwithstanding its small size this worm causes considerable disorders in its hosts--mostly children--as it sets up loss of appetite, diarrhœa, various nervous disturbances, and even epilepsy; all these symptoms, however, disappear after the expulsion of the parasites, which are generally present in large numbers.

The development as well as the manner of infection is still unknown; Grassi is of opinion that _Hymenolepis nana_ is indeed merely a variety of _Hymenolepis murina_, Duj., which lives in rats. According to Grassi direct development takes place with omission of the intermediate host, but with the retention of the larval stage; that is to say, rats infect themselves directly with _Hymenolepis murina_, by ingesting the mature segments or oncospheres of this species, from which subsequently the small larvæ originate in the intestinal wall (fig. 225); when fully developed they fall into the intestinal lumen and become tapeworms. The identity of the two forms has nevertheless been disputed (Moniez, R. Blanchard, v. Linstow), though their near relationship cannot be denied. Grassi gave mature segments of _Hymenolepis murina_ to six persons, but only one person evacuated a tapeworm. This, however, proves nothing in a district where _Hymenolepis nana_ frequently occurs in man; it was, moreover, not possible to infect rats with segments of _Hymenolepis nana_ (of man). Accordingly this form may represent an independent species, which, however, like _Hymenolepis murina_, also omits an intermediate host.

*Hymenolepis diminuta*, Rud., 1819.

Syn.: _Tænia diminuta_, Rud., 1819; _Tænia leptocephala_, Crepl.,
1825; _Tænia flavopunctata_, Weinld., 1858; _Tænia varesina_, E.
Parona, 1884; _Tænia minima_, Grassi, 1886.

This species measures 20 to 60 cm. in length, and up to 3·5 mm. in breadth; there are from 600 to 1,000 segments. The head is very small (0·2 to 0·5 mm.), it is club-shaped and has a rudimentary unarmed rostellum; the neck is short; the mature segments are 3·5 mm. in breadth, 0·66 mm. in length; the eggs are round or oval. The outer egg-shell is yellowish and thickened, with indistinct radial stripes; the inner embryonal shell (embryophore) double, thin; the outer layer is somewhat pointed at the poles; oncosphere 28 µ by 36 µ. Between the inner and outer shells is a middle granular layer.

_Hymenolepis diminuta_ lives in the intestine of rats--_Mus decumanus_ (the sewer rat), _Mus rattus_ (the black rat), and _Mus alexandrinus_, rarely in mice; it is occasionally also found in human beings.

Weinland described it from specimens collected by Dr. E. Palmer in 1842, in Boston, from a child aged 19 months, as _T. flavopunctata_. A second case relating to a three year old child, from Philadelphia, was only reported in 1889 by Leidy; a third case was simultaneously reported of a two year old girl in Varese (_T. varesina_); and Grassi described another case relating to a twelve year old girl from Catania (Sicily). Sonsino and Previtera reported the same species in Italy, Zschokke in France, Lutz and Magalhães in South America, and Packard in North America: a total of twelve cases, five from America, the rest from Europe (Ransom).

According to Grassi and Rovelli the larval stage lives in a small moth (_Asopia farinalis_), as well as in its larva, in an orthopteron (_Anisolabis annulipes_), and in coleoptera (_Acis spinosa_ and _Scaurus striatus_). Experimental infections have been successful on rats as well as on human beings. In America other species of insects may be the intermediary hosts.

Nicoll and Minchin[283] found in the body cavity of 4 per cent. of rat fleas (_Ceratophyllus fasciatus_) the cysticercoid of _Hymenolepis diminuta_. That it belonged to this species was shown by its unarmed rostellum and by feeding; 340 fleas were fed to white rats and fourteen worms obtained, _i.e._, about 4 per cent., thus corresponding to the infection of the fleas. The development in the flea probably begins in the pupal stage, the eggs being ingested by the older flea larvæ. The larva is 0·31 by 0·25 mm.; tail 0·8 mm., scolex 0·075 by 0·09 mm., suckers, 0·055 mm. in diameter. Microscopically it shows--(1) externally a radially striated layer resembling cuticle, (2) a layer of columnar cells, (3) parenchymatous layer continuous with the tail, (4) fibrous layer around the small caudal vesicle, then the parenchymatous scolex at the bottom of the secondary cavity.

[283] _Proc. Zool. Soc._, 1911, p. 9.

Nicoll and Minchin (_loc. cit._) found a cysticercoid[284] in the rat flea _Ceratophyllus fasciatus_ which was probably that of _Hymenolepis murina_. Body 0·16 mm., tail 0·19 mm., scolex 0·096 mm. in diameter. Rostellum has twenty-three spines in a single row. Length 0·017 mm., handle 0·01 mm., guard 0·007 mm., prong 0·007 mm. Sucker 0·042 mm. Although this cycle, then, for _H. murina_ also exists, it is not probable that rats (or man in the case of _H. nana_ if this be considered distinct) infect themselves in this way, as they hardly ingest all the necessary fleas to account for the massive infection which frequently exists in rats (and man), so that Grassi’s cycle holds good as the predominant method. _Xenopsylla cheopis_ has also been found by Johnston to harbour both cysticercoids in Australia.

[284] A third cysticercoid resembling this, but without hooks, has also been found.

*Hymenolepis lanceolata*, Bloch, 1782.

Syn.: _Tænia lanceolata_, Bloch, 1782; _Drepanidotænia lanceolata_,
Railliet, 1892.

The parasite measures 30 to 130 mm. in length and 5 to 18 mm. in breadth; the head is globular and very small; the rostellum is cylindrical, with a circlet composed of eight hooks (31 µ to 35 µ in length). The neck is very short. The short segments increase gradually and equally in breadth, but only a little in length; the female glands lie on the side opposite to that on which the genital pore is situated; the three elliptical testes are on the same side as the pores; the cirrus is armed and slender. The eggs have three envelopes and are oval (50 µ by 35 µ), the external envelope is thin, the middle intermediate layer or envelope is not so marked as in _H. diminuta_, and the internal one is very thin and sometimes has polar papillæ, as in _Hymenolepis diminuta_ and _H. nana_.

It inhabits the intestine of the following birds: Domesticated ducks and geese, the Muscovy duck (_Cairina moschata_), white-headed duck (_Erismatura leucocephala_), the pochard (_Nyroca rufina_), and the flamingo (_Phœnicopterus antiquorum_). It has been recorded from Great Britain, France, Denmark, Austria and Germany.

Zschokke reports the receipt of two specimens which a twelve year old boy in Breslau evacuated spontaneously at two different times.

The corresponding larva, according to Mrázek, lives in fresh water _Cyclops_; according to Dadai it is likewise found in another copepod, _Diaptomus spinosus_, but the hooks of Dadai’s larva differed in size.

Family. *Davaineidæ*, Fuhrmann, 1907.

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

Genus. *Davainea*, R. Blanch., 1891.

The large scolex is more or less globular, much wider than the
rostellum, which is furnished with two rings of very small and
numerous hooks. Neck absent, proglottids few, genitalia single.
Parasitic chiefly in birds.[285]

[285] [The larval stage of the Davaineas occurs in slugs (_Limax_) and snails (_Helix_).--F. V. T.]

*Davainea madagascariensis*, Davaine, 1869.

Syn.: _Tænia madagascariensis_, Dav.; _Tænia demerariensis_, Daniels,
1895.

This worm measures 25 to 30 cm. in length; the head has four large round suckers; the rostellum has ninety hooks (18 µ in length); there are 500 to 700 segments, of which the last 100 are filled with eggs and form half of the entire worm. The segments, when mature, measure 2 mm. in length by 1·4 mm. in breadth; genital pores unilateral; about fifty testes; the uterus consists of a number of loops, which at each side are rolled up into an almost spherical ball; when filled with eggs the convolutions unwind, permeate the segment and then lose their wall; the eggs lying free in the parenchyma become finally surrounded, one, or several together, by proliferating parenchymatous cells; this is how the 300 to 400 egg masses, taking up the entire mature segment, are formed. The globular oncosphere (8 µ) is surrounded by two perfectly transparent shells, the outer of which terminates in two pointed processes.

_Davainea madagascariensis_ has hitherto been found in man only (eight times). Davaine described this species from fragments sent to him from Mayotta (Comoro Islands), which were found in two Creole children. Chevreau observed four cases in Port Louis (Mauritius), likewise in children; Leuckart received the first perfect specimen--it was obtained from a three year old boy, the son of a Danish captain, in Bangkok; Daniels, at the _post-mortem_ of an adult native of George Town, Guiana, found two specimens (_Tænia demerariensis_); and finally Blanchard describes another perfect specimen which was in Davaine’s collection of helminthes in Paris, and which was obtained from a little girl 3 years old, of Nossi-Bé (Madagascar). The intermediate host is unknown.

*Davainea (?) asiatica*, v. Linst., 1901.

Syn.: _Tænia asiatica_, v. Linstow.

There exists only one headless specimen of this species, which is not quite adult, and which is preserved in the Zoological Museum of the Imperial Academy of Science in Petrograd. It came from a human being and was found by Anger in Aschabad (Asiatic Russia, near the northern frontier of Persia). The specimen measures 298 mm. in length. The breadth anteriorly is only 0·16 mm., the posterior part measures 1·78 mm. across. The number of segments is about 750. The genital pores are unilateral; the testes are globular and lie in a dorsal and ventral layer in the medullary layer; the cirrus pouch is pyriform, 0·079 mm. in length and 0·049 mm. in breadth; the female glands lie in the fore-part of the segments, the ovary reaching to the excretory vessels; the vitellarium is small and round. The vagina has a large fusiform receptaculum seminis; the uterus breaks up into sixty to seventy large, irregularly polyhedric eggsacs.

Family. *Tæniidæ*, Ludwig, 1886.

Genus. *Tænia*, L., 1758.[286]

With the characters of the family. In the genus Cladotænia recognized
by some authors, the testes encroach on the mid field and the uterine
stem reaches the anterior end of the segment.

[286] The Greeks termed the tapeworms ἕλμινθες πλατεῖαι, more rarely χηρία (= fascia); the Romans called them _tænia_, _tinea_, _tæniola_, later _lumbrici_, usually with the addition _lati_, to distinguish them from the _Lumbrici teretes_ (_Ascaridæ_). The proglottids were called _Vermes cucurbitini_; the cysticerci χάλαζαι (hailstones), later hydatids. Plater (1602) was the first to differentiate _Tænia intestinorum_ (= _Bothriocephalus latus_) amongst the _Lumbrici lati_ of man from _Tænia longissima_ (= _Tænia solium_). The term _solium_ was already used by Arnoldus Villanovanus, who lived about 1300; and, according to him, it signifies “cingulum” (belt, chain), while N. Andry, in 1700, traces this word from “solus,” because the worm occurs always singly in man. Leuckart and Krehl derive the word “solium” from the Syrian “schuschl” (the chain), which in Arabian has become “susl” or “sosl,” and in Latin has become “sol-ium.” What Linnæus described under the term _Tænia solium_ was really _Tænia saginata_; the latter was first distinguished by Goeze, but was forgotten until Küchenmeister, in 1852, again called attention to the differences.

*Tænia solium*, L., _p. p._, 1767.

Syn.: _Tænia cucurbitina_, Pall., 1781; _Tænia pellucida_, Goeze,
1782; _Tænia vulgaris_, Werner, 1782; _Tænia dentata_, Gmel., 1790;
_Halysis solium_, Zeder, 1800; _Tænia humana armata_, Brera, 1802;
_Tænia_ (_Cystotænia_) _solium_, Lkt., 1862.

The average length of the entire tapeworm is about 2 to 3 m., but may be even more; the head is globular, 0·6 to 0·8 to 1·0 mm. in diameter. The rostellum is short with a double circlet of hooks, twenty-two to thirty-two in number, usually twenty-six to twenty-eight; large and small hooks alternate regularly; the length of the large hooks is 0·16 to 0·18 mm., of the small ones 0·11 to 0·14 mm. The rostellum is sometimes pigmented. The suckers are hemispherical, 0·4 to 0·5 mm. in diameter. The neck is fairly thin and long (5 to 10 mm.). The proglottids, the number of which averages from 800 to 900, increase in size very gradually; at about 1 m. behind the head they are square and have the genitalia fully developed. Segments sufficiently mature for detachment measure 10 to 12 mm. in length by 5 to 6 mm. in breadth. The genital pores alternate fairly evenly at the lateral margin a little behind the middle of each segment. The fully developed uterus consists of a median trunk, with seven to ten lateral branches at either side, some of which are again ramified. The eggs are oval, the egg-shell very thin and delicate; the embryonal shell (embryophore) is thick, with radial stripes; it is of a pale yellowish colour, globular, and measures 31 µ to 36 µ in diameter; the oncospheres, with six hooks, are likewise globular, and measure 20 µ in diameter (fig. 238).

Malformations are not so common as in _T. saginata_; they consist in
two or several proglottids being partly or entirely fused, formation
of single club-shaped segments, fenestration of long or short series
of segments and so-called double formation, in which the head has six
suckers and the segments exhibit a *Y*-shaped transverse section. The
oncospheres occasionally also possess more than six hooklets. Very
slender specimens have led to the description of a particular species
or variety (_T. tenella_).

In its fully developed condition _T. solium_ is found exclusively in man; the head is usually attached in the anterior third of the small intestine and the chain, in numerous convolutions, extends backwards; a few mature detached proglottids usually lie at the most posterior part, and these are usually evacuated during defæcation. In exceptional cases single proglottids or whole worms may reach contiguous organs if abnormal communications with them exist; thus they may reach the abdominal cavity and the urinary bladder, or they may be found in a so-called worm abscess of the peritoneum; occasionally, in vomiting, single segments or several together may be brought up. Exceptionally it induces severe anæmia.

The _larval stage_ (_Cysticercus cellulosæ_) that gives rise to _Tænia solium_ lives normally in the intramuscular connective tissue and other organs of the domestic pig, but it is known to exist also in a few other mammals, such as the wild boar, the sheep,[287] the stag, dog, cat, brown bear and monkey, as well as in man. The cysticercus of the pig is an elliptical vesicle with a longitudinal diameter of 6 to 20 mm., and a transverse diameter of 5 to 10 mm.

[287] The larvæ which on rare occasions are found in the muscular system of sheep are either strayed specimens of _Cysticercus tenuicollis_, which normally develop in organs of the abdominal cavity, and appertain to _Tænia marginata_ of the dog, or actually _Cysticercus cellulosæ_. (_Cf._ Bongert, in _Zeitschr. f. Fleisch- u. Milchhyg._, 1899, ix, p. 86.)

Even with the naked eye a white spot may be observed in the centre of the long equator, this being the invaginated head; it is easy to make it project by pressing on the vesicle (after tearing off with the finger-nail the investing connective tissue), and on examining it under the microscope one can convince oneself that it corresponds with the head of _Tænia solium_.

Numerous experiments have proved that the _Cysticercus cellulosæ_ of the pig, if introduced into the intestine of man, grows to a _Tænia solium_ (Küchenmeister, 1855; Humbert, 1856; Leuckart, 1856; Hollenbach, 1859; Heller, 1876); the cysticercus has frequently also been cultivated purposely by feeding pigs with mature proglottids of _T. solium_ (P. J. van Beneden, 1853; Haubner and Küchenmeister, 1855; Leuckart, 1856; Mosler, 1865; Gerlach, 1870; etc.), but success did not attend the efforts to make _Cysticercus cellulosæ_ establish themselves in the intestines of pigs, dogs, guinea-pigs, rabbits and monkeys (_Macacus cynomolgus_), and so become adult Tæniæ; the attempts, also, to infect dogs with cysticerci by means of ova were likewise, as a rule, abortive.[288]

[288] According to Gerlach only young pigs (up to 6 months old) are capable of infection, and perhaps the failure may have been due to the animals chosen for experiment being of the wrong age.

The development of _Cysticercus cellulosæ_ takes two and a half
to three or four months; it is not known how long the cysticerci
remain alive in animals; not uncommonly they perish at earlier or
later stages, and become calcified or caseated. Extracted cysticerci
die in water at a temperature of 47° to 48° C., in flesh at normal
temperature they remain alive for twenty-nine days or more. On
account of the present rapid means of pickling and smoking meat, the
cysticerci as a rule are not killed, also the effect of cold on them
for some time in cold chambers of slaughterhouses is not lethal, but
freezing is fatal (Ostertag).

There is not the least doubt that human beings are almost exclusively infected with _Tænia solium_ by eating pork containing cysticerci in a condition that does not endanger the life of the cysticerci. The infection may likewise be caused in man by eating the infected meat of other animals subject to this species of bladder worm, mainly, as a matter of fact, deer and wild boar.

The frequency of cysticerci in pigs’ flesh has considerably decreased
since the introduction of meat inspection; in the Kingdom of Prussia
there was on an average 1 infected pig to every 305 slaughtered
between 1876 to 1882; from 1886 to 1889, there was 1 to 551; from
1890 to 1892, there was 1 to 817; in 1896, 1 to 1,470; and in 1899, 1
to 2,102; in the Kingdom of Saxony in 1894 there was 1 infected pig
to every 636; in 1895 there was 1 to every 2,049, and in 1896 only 1
infected pig was found of 5,886 slaughtered. In South Germany pigs
with cysticerci are very rare, but are more frequent in the eastern
provinces of Prussia; in 1892 the number of infected pigs compared
with the total slaughtered was as follows:--

In the district of Marienwerder 1 : 28
" " Oppeln 1 : 80
" " Königsberg 1 : 108
" " Stralsund and Posen 1 : 187
" " Danzig, Frankfort a. O. and Bromberg 1 : 250
As compared with the district of Arnsberg 1 : 865
" " " Coblenz 1 : 975
" " " Düsseldorf 1 : 1,070
" " " Münster and Wiesbaden 1 : 1,900

The average for the whole of Prussia in the same year was 1 : 1,290;
for the eastern provinces, on the other hand, 1 : 604. Even more
unfavourable are the proportions in Russian Poland (over 1 per
cent. of pigs measly), in Prague (over 3 per cent.), in Bosnia and
Herzegovina (6 to 7 per cent.). The cause for this is most likely
attributable to the manner in which the pigs are kept. When allowed
to be in the farmyards of the small farmers for the whole day, or
allowed to wander in the village streets and pasture lands, they are
more liable to take up the oncospheres of the _T. solium_ than when
shut up in good pig-styes.

The geographical distribution of _T. solium_ generally corresponds with that of the domestic pig and the custom of eating pork in any form insufficiently cooked or raw. There are, or were, some isolated districts in Germany, France, Italy and England where the “armed tapeworm” was frequent (for instance, Thuringia, Brunswick, Saxony, Hesse, Westphalia, whereas it is and was very scarce in South Germany); it is thus easily understood why it occurs very rarely in the East, in Asia and in Africa, in consequence of the Mahommedans, Jews, etc., not eating pork. In North America, also, _T. solium_ is very rare; the tapeworm which is known there by this name is generally _T. saginata_, Stiles. During the last decade _T. solium_ infection has, however, very markedly decreased in North and East Germany in consequence of the precautions exercised by the public in the choice of pork to avoid trichinosis, especially, however, because measly meat must be sold as such and must be thoroughly cooked before being placed on the market; indeed, if badly infected it may not be sold for food, but can be turned to account for industrial purposes.

The occurrence of _Cysticercus cellulosæ_ in man has been known since 1558 (Rumler, _Obs. med._, liii, p. 32); there is hardly an organ in man in which cysticerci have not been observed at some time; they are most frequently found in the brain,[289] where they grow to a variety known as _Cysticercus racemosus_; next in frequency they are found in the eye, in the muscular system, in the heart, in the subcutaneous connective tissue, the liver, lungs, abdominal cavity, etc. The number of cysticerci observed in one man varies between a few and several thousands. Of the sexes, men are most subject (60 to 66 per cent. of the number attacked). The disturbances caused in man by cysticerci vary according to the nature or position of the organs attacked; when situated in the cerebral meninges they have the same effect as tumours.

[289] Dressel, for instance, examined eighty-seven persons suffering from cysticercus, and found it seventy-two times in the brain, thirteen times in the muscles; K. Müller, in thirty-six cases, found it twenty-one times in the brain, twelve times in the muscles, three times in the heart; Haugg, in twenty-five cases, found it thirteen times in the brain, six times in the muscles, twice in the skin, etc. According to Graefe, amongst 1,000 ophthalmic cases in Halle and Berlin, there was one with cysticercus in the eye; in Stuttgart there was only one in 4,000, in Paris one in 6,000, and in Copenhagen one in 8,000.

During the last decades, however, these cases have also become less common. In Rudolphi’s time 2 per cent. of _post-mortems_ in Berlin showed cysticerci; in the ’sixties, according to Virchow, about the same; in 1875 the number fell to 1·6 per cent.; in 1881 to 0·5 per cent.; in 1882 to 0·2 per cent.; in 1900 to 0·15 per cent., and in 1903 to 0·16 per cent. Hirschberg between 1869 and 1885 discovered cysticerci in the eye seventy times in 60,000 ophthalmic cases, but during the following six years the parasite was only present twice amongst a total of 46,000 cases of ophthalmic diseases, and since 1895 no ophthalmic case has been met with.

The infection of human beings with the cysticerci can only take place by the introduction of the oncospheres of _Tænia solium_ into the stomach with vegetable foods, salads that have been washed in impure water containing oncospheres, also by drinking contaminated water; the carriers of _T. solium_, moreover, infect themselves still more frequently through uncleanliness in defæcation, the privies in public localities and many private houses affording striking testimony of this. The minute oncospheres can thus easily reach the fingers and thence the mouth (as in twirling the moustache, biting the nail). More rarely a third manner of transmission or internal auto-infection may possibly take place, as when, in the act of vomiting, mature proglottids near the stomach are drawn into it; the oncospheres or segments there retained are then in the same position as if they had been introduced through the mouth.

On account of these dangers of internal or external auto-infection,
it is therefore the duty of the medical attendant, after recognizing
the presence of tapeworms, to expel them,[290] and in doing so to
employ every possible means to prevent vomiting setting in; it is,
however, equally important to take the necessary steps to destroy the
parasites evacuated. It may be incidentally mentioned that in using
certain remedies the scolex not rarely remains in the intestine; the
cure in such cases has not been accomplished, as the scolex again
produces new proglottids, and after about eleven weeks the first
formed ones are again mature and appear in the fæces.

[290] The diagnosis as a rule is not difficult; the patients themselves frequently observe the pumpkin seed-like segments in the fæces. But in such cases the diagnosis must still be confirmed. In other cases the discovery of the oncospheres in their embryonal shells (embryophores), which cannot be confounded with the other constituents of the fæces, gives complete certainty, although the differential diagnosis between _T. solium_ and _T. saginata_ is hardly possible from the embryophores; but, if evacuated segments are placed between two slides and lightly pressed, the species is easily recognizable by the shape of the uterus (_cf._ figs. 239 and 241).

Amongst the cysticerci also many malformations appear; thus absence
of the rostellum and the hooks, or double formation with six suckers,
or abnormalities of growth on account of the surroundings, which have
had a special name given to them, _viz._, _Cysticercus racemosus_,
Zenk. (= _C. botryoides_, Hell.; _C. multilocularis_, Kchnmstr.);
these forms are more especially found at the base of the brain, are
irregularly ramified and often without the head.

A certain interest is attached to those forms that have led to the establishment of a distinct species:--

*Cysticercus acanthotrias*, Weinld., 1858.

In making the autopsy of a white Virginian woman who had died of
phthisis, a cysticercus was found in the dura mater, and eleven or
twelve specimens in the muscles and subcutaneous tissue. Weinland
and Leuckart, who examined the specimens, found that they resembled
_Cysticercus cellulosæ_ in form and size, but that they carried on
the rostellum a triple crown, each consisting of fourteen to sixteen
hooks, which differed from the hooks of _C. cellulosæ_ or of _Tænia
solium_ by the greater length of the posterior root process and the
more slender form of the hooks; the large hooks measured 0·153 to
0·196 mm., the medium-sized hooks, 0·114 to 0·14 mm., and the small
ones 0·063 to 0·07 mm.

On account of these differences a distinct species of cysticercus was established, and this naturally presupposed a corresponding species of Tænia (_T. acanthotrias_, Lkt.); this could be done with justice so long as the case remained isolated, _i.e._, in America, as there was the possibility of the corresponding Tænia being found. In this respect, however, the position has changed; Delore first described a cysticercus the size of a nut from the biceps muscle of the arm of a silk-worker in Lyons; according to Bertolis this specimen possessed hooks of three different sizes, the dimensions of which corresponded with the figures given by Weinland and Leuckart; the correctness of the diagnosis could hardly be doubted, as Bertolis was known to be a very exact observer. A second case has become known through Cobbold, who regards a specimen of a cysticercus in Dallinger’s collection as likewise belonging to _Cysticercus acanthotrias_; this specimen also came from a man’s brain; finally a third case, also from France, has been published by Redon. This author, amongst numerous _C. cellulosæ_ of a man, found one that had forty-one hooks in three rows, and he was the first to express the opinion that _C. acanthotrias_ does not represent a distinct species, but is only an abnormality of _C. cellulosæ_. This view was also taken by Blanchard and Railliet, and is probably correct, as the discovery of the large corresponding Tænia furnished with three rows of hooks is not to be expected in European beasts of prey, and in Redon’s case _C. acanthotrias_ as well as _C. cellulosæ_ occurred simultaneously.

The duration of life of _C. cellulosæ_ in man is very long; cysticerci of the eye have been known to persist for twenty years, and in cysticercus of the brain ten to nineteen years may elapse from the first appearance of cerebral symptoms until death. Dead cysticerci may shrivel up or become calcified, perhaps also undergo fatty degeneration and then absorption. Finally, it may be mentioned that if particular proof is required that _C. cellulosæ_ of man belongs to the cycle of development of the _Tænia solium_, such proof has been furnished by Redon.

NOTE.--_Tænia tenella_, mentioned on p. 332, was ascribed by Cobbold
to cysticerci of the muscular system of sheep. It has, however,
been demonstrated that these cysticerci belong to the cycle of
development of _Tænia marginata_ (dog) (_Cysticercus tenuicollis_,
from the omentum of sheep); but as already stated _C. cellulosæ_ also
occurs in sheep. Chatin himself swallowed the cysticercus, which
Cobbold termed _C. ovis_, without causing a Tænia to develop in his
intestine. Müller also vainly sought to induce infection with _C.
tenuicollis_ in his own person. On the other hand, the feeding of
a dog with _Cysticercus ovis_ resulted in the production of _Tænia
marginata_.

*Tænia bremneri*, Stephens, 1908.

Characterized by the large size of the gravid segments. The largest was 32 by 9 mm. Smallest 21 by 6 mm. Average 28·6 by 8·5 mm. Mode 21 by 6 mm. Uterine branches twenty-two to twenty-four in number. Calcareous bodies numerous, 15·2 µ in diameter. Eggs maximum 45·6 µ by 41·8 µ. Smallest 34·2 µ by 30·4 µ. Mode 38 µ by 30·4 µ.

*Tænia marginata*, Batsch, 1786.

Syn.: T. e. _Cysticerco tenuicolli_, Küchenmeister, 1853.

This species, which in structure resembles _Tænia solium_, lives
in the intestine of the dog and the wolf. It attains 1·5 to 4 m.
in length, possesses a double crown of thirty to forty hooks, on
an average thirty-six to thirty-eight hooks, and in its larval
stage (_Cysticercus tenuicollis_) lives in the peritoneal cavity of
ruminants and the pig, occasionally in the monkey and squirrel.

It is included in this work because, according to one statement,
_C. tenuicollis_ is supposed to have been observed in man in North
America; but the case is not quite certain, as the number of hooks
was less than in _C. tenuicollis_ and coincided with _C. cellulosæ_,
although the size of the cysticercus appeared to point to _C.
tenuicollis_. A yet earlier statement of Eschricht, that _Cysticercus
tenuicollis_ had been observed in Iceland in the liver of a man, is
undoubtedly due to an error.

*Tænia serrata*, Goeze, 1782.

This parasite attains a length of from 0·5 to 2 m., possesses a
double crown of thirty-four to forty-eight (mostly forty) hooks. It
lives exclusively in the intestine of the dog, the corresponding
cysticercus (_Cysticercus pisiformis_) living in the mesentery of the
hare and rabbit. We mention this species with all reserve amongst
the parasites of man, because Vital states that he has observed it
twice in Constantine (Algeria) in human beings. The data, however,
are not sufficient to characterize the species. It is highly probable
that they relate to _Tænia solium_. Galli-Valerio even swallowed five
specimens of _Cysticercus pisiformis_, but without result.

*Tænia crassicollis*, Rud., 1810.

I only mention this species from the intestine of the domestic cat
because Krabbe regards its occurrence in man as possible. It attains
a length of 60 cm. and is armed; its cysticercus (_Cysticercus
fasciolaris_) lives in the liver of mice and rats. In Jutland,
according to Krabbe, chopped-up mice (spread on bread) are eaten
raw, being a national remedy for retention of urine, and this custom
affords the possibility of the introduction of _C. fasciolaris_ into
the intestine of man (_Nord. med. Arkiv_, 1880, xii).

*Tænia saginata*, Goeze, 1782.

Syn.: _Tænia solium_, L., 1767 (_pro parte_); _Tænia cucurbitina_,
Pallas, 1781 (p.p.); _Tænia inermis_, Brera, 1802. Moquin-Tandon,
1860; _Tænia dentata_, Nicolai, 1830; _Tænia lata_, Pruner,
1847; _Bothriocephalis tropicus_, Schmidtmuller, 1847; _Tænia
mediocanellata_, Küchenmeister, 1855; _Tænia zittavensis_,
Küchenmeister, 1855; _Tænia tropica_, Moquin-Tandon, 1860; _Tænia_
(_Cystotænia_) _mediocanellata_, Leuckart, 1863.

The length of the entire tapeworm averages 4 to 8 to 10 m. and more, even up to 36 m. According to Bérenger-Feraud it attains a length of 74 m. (?) The head is cubical in shape, 1·5 to 2 mm. in diameter; the suckers are hemispherical (0·8 mm.) and are frequently pigmented; there is a sucker-like organ in place of the rostellum, and this also is frequently pigmented. The neck is moderately long and about half the breadth of the head; the proglottids, the number of which averages more than 1,000, gradually increase in size; the mature detached segments are shaped exactly like pumpkin-seeds, and are about 16 to 20 mm. in length and 4 to 7 mm. in breadth. The genital pores alternate irregularly and are situated somewhat behind the middle of the lateral margin. There are twenty to thirty-five lateral branches at each side of the median trunk of the uterus, and these again ramify. The eggs are more or less globular, the egg-shell frequently remains intact and carries one or two filaments; the embryonal shell (embryophore) is thick, radially striated, is transparent and oval; it is 30 µ to 40 µ in length, and 20 µ to 30 µ in breadth. Several segments simultaneously are usually passed spontaneously with defæcation.

Malformations are not uncommon, and resemble those of _Tænia solium_;
a triangular form has been termed _T. capensis_ by Küchenmeister, and
_T. lophosoma_ by Cobbold, names that naturally possess as little
value as does the term _T. fenestrata_ for fenestrated specimens.
Moreover, _T. solium_, var. _abietina_, Weinld., 1858, which was
evacuated by an Indian, was probably a _T. saginata_ with somewhat
close uterine branches. It is regarded by Stiles and Goldberger as a
doubtful subspecies.

_T. saginata_ in its adult condition lives exclusively in the intestinal canal of man.[291] The corresponding cysticercus is _Cysticercus bovis_, and is found almost exclusively in the ox; it is small, 7·5 to 9 mm. in length and 5·5 mm. in breadth, may easily escape notice, and requires from three to six months for its development. Numerous experiments have confirmed the connection of _Cysticercus bovis_ with _Tænia saginata_; indeed, the cysticercus was only discovered by feeding experiments after attention had been called to the ox as the probable intermediary host of this Tænia.

[291] Abnormal migrations of this species have also been known. Compare, amongst others, Stieda, A., “Durchbohr. d. Duod. u. d. Pancreas durch eine Tænia,” _Centralbl. f. Bakt., Path. und Infektionsk._, 1900, xxviii (1), p. 430.

Medical men observed that weakly children who were ordered to eat
raw scraped beef to strengthen them contracted _T. saginata_. It
was found, moreover, that Jews, who are prohibited from eating pork
from religious motives, suffered especially from _T. saginata_;
when _T. solium_ was found to occur in a Jew he often confessed to
having eaten pork; and finally it was found that certain nations--for
instance, the Abyssinians--frequently harbour _T. saginata_, and only
eat beef--raw by preference.

These observations led Leuckart, in 1861, to feed young calves
with the proglottids of _T. saginata_ in order to discover the
corresponding cysticercus, which was then not known. This experiment
was successful. Similar experiments, with similar results, were
then conducted by Mosler (1863), Cobbold and Simonds (1864 and
1872), Röll (1865), Gerlach (1870), Zürn (1872), Saint Cyr, Jolicœur
(1873), Masse and Pourquier (1876), and Perroncito, in 1876. The
attempts to infect goats, sheep, dogs, pigs, rabbits and monkeys were
unsuccessful. Only Zenker and Heller were able to infect kids, and
Heller infected one sheep, but these are exceptions.

Artificial infections of human beings with _Cysticercus bovis_ to obtain the tapeworm were less numerous, and indeed quite superfluous, yet this was also done by Oliver (1869) in India, and Perroncito (1877) in Italy. The experiments of the latter prove that the extracted cysticerci of the ox certainly perish in water at 47° to 48° C.

It is a remarkable circumstance that, at least as regards Central
Europe, _C. bovis_ in the ox, after natural infection, was so seldom
found that almost every case was published as a rarity; whereas the
Tænia is very frequent in man. The reason for this is that in Germany
cattle are not severely infected, and that the small, easily dried-up
cysticerci easily escape notice in the large body of the host.
Hertwig, the late director of the town cattle market in Berlin, in
1888, pointed out that the cysticercus of the ox is found chiefly in
the musculi pterygoide externi and interni, and since that time a far
greater number of infected oxen have been found in Berlin.

---------+----------------+----------+------------
Year | Number of oxen | Infected | Proportion
| slaughtered | |
---------+----------------+----------+------------
1888–89 | 141,814 | 113 | 1 : 1,255
1889–90 | 154,218 | 390 | 1 : 395
1890–91 | 124,593 | 263 | 1 : 474
1891–92 | 136,368 | 252 | 1 : 541
1892–93 | 142,874 | 214 | 1 : 672
---------+----------------+----------+------------

Since 1892 an increase has taken place in the number of oxen infected
with cysticercus, but this is probably attributable to the more
general and searching examinations. In the slaughter-houses of
Prussia the number of infected beasts was as follows:--

1892 567
1893 686
1894 748
1895 1,143
1896 1,981
1897 2,629

The condition was most frequent in Neisse (3·2 to 4 per cent.),
Eisenach (1·91 per cent.), Ohlau (1·57 per cent.), Oels i. Schles.
(1 per cent.), Marienwerder (0·34 to 1·2 per cent.). The flesh of
oxen only slightly infected (containing not more than ten living
cysticerci) is sold in pieces of not more than 5 lb. to consumers
after having been rendered innocuous by cooking, or by pickling for
twenty-one days in 25 per cent. salt brine, or hanging for twenty-one
days in suitable refrigerators; oxen in which only one cysticercus is
found are allowed free commerce, and those strongly infected (_i.e._,
containing more than ten living cysticerci) may only be used for
industrial purposes.

It is a striking fact that more bulls than cows are infected
(according to Reissmann, in Berlin, from 1895 to 1902, 0·446 per
cent. bulls, 0·439 per cent. oxen, and 0·262 per cent. cows), the
explanation of which, according to Ostertag, is that most oxen are
killed when young, when also infection most readily takes place, and,
further, that the larva later on in life can be completely atrophied.

The cysticercus of the ox has hitherto been found in man on very rare occasions. Arndt (_Zeitschr. f. Psychiat._, xxiv) mentions a case in the brain, Heller in the eye, and Nabiers and Dubreith also in the brain (_Journ. méd. Bordeaux_, 1889–1890, p. 209); but the diagnoses are not quite certain, as absence of hooks occasionally occurs in _Cysticercus cellulosæ_.

_Tænia saginata_ is the most frequent tapeworm of man (with the exception of _Dibothriocephalus latus_ in a few districts), and the parasite is widely distributed over the surface of the globe; it has been known in the East for ages, so far as data are available; it is frequent in Africa, America, and Europe. Its frequency has perceptibly increased during the last few years, but a decrease should soon take place in consequence of the extent and improvement of the official inspection of meat.

The following table shows the relative frequency of the Cestodes of man:--

----------------+---------+----------+----------+-------+------+-------+--------
| |Number of | _T. | _T. |_Dibr.|_Dipyl.|Undeter-
Author | Year | cases |saginata_ |solium_|latus_|canin._| mined
----------------+---------+----------+----------+-------+------+-------+--------
Parona (Milan) | 1899 | 150 | 121 | 11 | 4 | -- | 14
Parona (Italy) | 1868–99 | 513 | 397 | 71 | 26 | -- | 19
Krabbe (Denmark)| 1869 | 100 | 37 | 53 | 9 | 1 | --
" " | 1869–86 | 200 | 153 | 24 | 16 | 8 | --
" " | 1887–95 | 100 | 89 | -- | 5 | 6 | --
" " |1896–1904| 50 | 41 | 1 | 5 | 3 | --
Blanchard | 1895 | ? | 1,000 | 21 | -- | -- | --
(Paris) | | | | | | |
Stiles | 1895 |{more than|more than}| -- | 3 | -- | --
(United States)| |{ 300 | 300 }| | | |
Schoch | 1869 | 19 | 16 | 1 | 2 | -- | --
(Switzerland) | | | | | | |
Zaeslein | 1881 | ? | 180 | 19 | ? | |
(Switzerland) | | | | | | -- | --
Kessler | 1888 | ? | 22 | 16 | 47 | -- | --
(Petrograd) | | | | | | |
Mosler | 1894 | 181 | 112 | 64 | 5 | -- | --
(Greifswald) | | | | | | |
Bollinger | 1885 | 25 | 16 | 1 | 8 | -- | --
(Munich) | | | | | | |
Vierordt | 1885 | 121 | 113 | 8 | -- | -- | --
(Tübingen) | | | | | | |
Mangold | 1885–94 | 128 | 120 | 6 | 8 | -- | --
(Tübingen) | | | | | | |
----------------+---------+----------+----------+-------+------+-------+--------

*Tænia africana*, v. Linst., 1900.

This worm measures over 1·3 m. in length. The segments are all broader than they are long. The scolex is unarmed and is provided with an apical sucker (0·16 mm.). The parasite measures 1·38 mm. in breadth, 1·03 mm. in width; the suckers measure 0·63 mm. in diameter. The neck is very short and somewhat broader than the scolex; number of segments about 600; the hindmost segments measure 7 mm. in length and 12 to 15 mm. in breadth. The genital pores alternate irregularly in the middle of the lateral margin; the testes are very numerous and occupy the entire medullary layer; the vas deferens is much convoluted; the cirrus pouch is pyriform and thick walled; the cirrus and vagina are beset with bristles directed outwards; the receptaculum seminis is fusiform; the ovary is large and double, and consists of radially placed club-shaped tubes that do not anastomose and do not branch; the vitellarium is at the posterior border of the proglottids, the round shell gland in front of it; the uterus consists of a median trunk and fifteen to twenty-four non-ramified lateral branches on each side; the embryonal shell is thick and has radial stripes--it may be round (31·2 µ to 33·8 µ) or oval (39 µ, by 33·8 µ); the spines of the oncospheres measure 7 µ to 8 µ in length (fig. 197).

At present only two specimens are known; they came from a black soldier from the vicinity of Lake Nyasa. The cysticercus is unknown; perhaps it lives in the zebu, the flesh of which the Askaris are in the habit of devouring uncooked.

*Tænia confusa*, Ward, 1896.

Length 8·5 m., breadth about 5 mm. The scolex is unknown; there is no neck; number of proglottids 700 to 800, always longer than they are broad; the hindmost measure 35 mm. in length, 4 to 5 mm. in breadth; the genital pores alternate irregularly behind the middle of the lateral margin; testicles numerous; vas deferens not much coiled; the cirrus pouch thick walled, elongated and club-shaped, with globular vesicula seminalis; the cirrus is beset with little hairs; the receptaculum seminis is globular; ovary small, double; each half is bean-shaped; vitellarium narrow, triangular; shell gland globular; uterus with median trunk and fourteen to eighteen short ramified lateral branches on either side. The embryophores are oval (39 µ by 30 µ), thick and radially striated.

Of this species only two specimens have been recorded; they occurred in human beings and were sent at different times to the first describer of them by a doctor in Lincoln (Nebr.). Perhaps _Tænia solium_, var. _abietina_, Weinld., which was found in a Chipeway Indian, is of the same species in spite of the shorter segments.

*Tænia echinococcus*, v. Sieb., 1853.

Syn.: _Tænia nana_, v. Ben., 1861 (_nec_ v. Sieb., 1853);
_Echinococcifer echinococcus_, Weinld., 1861.

_Tænia echinococcus_ measures 2·5 to 5 or 6 mm. in length; the head is 0·3 mm. in breadth, and has a double row of twenty-eight to fifty hooklets (on an average thirty-six to thirty-eight) on the rostellum.

The size and form of these hooklets vary (the larger ones are 0·040 to 0·045 mm. in length, the smaller ones are 0·030 to 0·038 mm. in length). The suckers measure 0·13 mm. in diameter; the neck is short; there are only three or four segments, the posterior segment being about 2 mm. in length and 0·5 mm. in breadth. The genital pores alternate; there are forty to fifty testicles; the vas deferens is spirally coiled; the cirrus pouch is pyriform. The ovary is horseshoe-shaped with the concavity directed backwards; the vitellarium double, each half almost bean-shaped, at right angles to the plane of the segment; the shell gland is round. The median trunk of the uterus is dilated when filled with eggs and (instead of lateral branches) has lateral diverticula. It is not unusual for the eggs to form local heaps. The embryonal shell (embryophore) is moderately thin, with radial striæ, almost globular, 30 µ to 36 µ in diameter.

When mature this parasite lives in the small intestine of the domestic dog, the jackal, and the wolf, and apparently also in _Felis concolor_, and is usually present in great numbers; it can also be transmitted experimentally to the domestic cat, one successful result out of seven (Dévé).[292] The larval stage (_Echinococcus polymorphus_) lives in various organs--chiefly in the liver and lungs--of numerous species of mammals (twenty-seven), especially in sheep, ox and pig, and it is even not uncommon in man, though the Tænia itself has never been found in a human being; accordingly man can only acquire the echinococcus by ingesting the eggs of the “dog worm.” The dogs disseminate the eggs of _Tænia echinococcus_ wherever they go, or carry them to their mouths and coats by biting up the evacuated segments, and are thus able to transmit them directly to human beings (by licking them or making use of the same crockery, etc.). In other cases the oncospheres, enclosed in the embryophores, must withstand desiccation for a time and then (as when the dogs are “kissed” or otherwise caressed) are transmitted into or on to man. As echinococcus disease in man is always very dangerous, it would be a matter of general interest to prevent dogs being infected by destroying the echinococci,[293] and all measures would be justifiable which would diminish the superfluous number of house-dogs (for instance, high taxes); measures should also be adopted to limit the association of men with dogs, particularly in such frequented places as restaurants, railway carriages and tram-cars.

[292] In Iceland 28 per cent. of the dogs are infected with this Tænia, in Lyons 7·1 per cent., in Zurich 3·9 per cent., in Berlin 1 per cent., and in Copenhagen 0·4 per cent. In Australia even 40 to 50 per cent. of the dogs are affected. It is, however, a question whether, in addition to _Tænia echinococcus_, a second analogous form is not involved, as the form from _Canis dingo_ attains a length of 10 to 30 mm.

[293] Mosler, F., “Ueb. Mittel z. Bekampfg. endem. vork. Echinococcuskrank.,” _Deutsch. med. Zeit._, 1889, No. 72.

Echinococcus is very common in slaughtered animals; in Germany,
however, the figures in the reports of the abattoirs present an
erroneous view in so far as, besides the total number of animals
slaughtered, only the numbers of those organs (liver and lungs) are
published that were so severely infected with echinococci that, even
when the parasites were “shelled” out, the flesh could not be placed
upon the market and was therefore “condemned.”

In Berlin the following animals were slaughtered:--

-------+---------+---------+---------+---------+---------+---------
Year | 1889–90 | 1890–91 | 1891–92 | 1892–93 | 1896–97 | 1902
-------+---------+---------+---------+---------+---------+---------
Oxen | 154,218 | 124,593 | 136,368 | 142,874 | 146,612 | 153,748
Sheep | 430,362 | 371,943 | 367,933 | 355,949 | 395,769 | 434,155
Pigs | 442,115 | 472,859 | 530,551 | 518,073 | 694,170 | 778,538
-------+---------+---------+---------+---------+---------+---------

During the same years the following were condemned in consequence of
being infected with echinococci:--

-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+-----
|Lung |Liver|Lung |Liver|Lung |Liver|Lung |Liver|Lung |Liver|Lung |Liver
-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+-----
Oxen |7,266|2,418|5,792|1,938|4,497|1,721|2,563| 739|3,284|1,156| 2,507| 791
Sheep|5,479|2,742|4,595|2,059|4,435|1,669|3,331|1,161|4,561|1,939|11,138|4,437
Pigs |6,523|5,078|5,083|3,735|6,037|4,374|6,785|4,312|7,888|5,398| 9,544|9,233
-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+-----

Nevertheless there are statistics that give the total number of
animals infected with echinococcus:--

--------+-------------+--------------+--------------+--------------
Author | Place | Oxen | Sheep | Pigs
--------+-------------+--------------+--------------+--------------
Längrich|Rostock i. M.|26·2 per cent.|37·0 per cent.| 5·4 per cent.
Olt |Stettin | 7·1 " |25·8 " | 7·3 "
Steuding|Gotha |24·6 " |35·4 " |21·4 "
Prettner|Prague |23·2 " | 5·5 " | ?
--------+-------------+--------------+--------------+--------------

In Güstrow, in Mecklenburg, half of the animals slaughtered are said
to be infected with echinococcus; in Wismar 25 per cent. of the oxen,
15 per cent. of the sheep and 5 per cent. of the pigs are infected;
according to Mayer, in Leipzig, 3·79 per cent. native pigs, 24·47
per cent. Hungarian pigs, and 13·09 per cent. of sheep were infected
with echinococcus; at the same time it was stated that in regard
to the native pigs the liver was more frequently affected than the
lungs (3·81 per cent. as compared with 0·26 per cent.); in sheep the
lungs were more frequently infected (12·71 per cent. to 3·73 per
cent.), whereas in the Hungarian pigs both organs were almost equally
infected (14·78 per cent. to 12·03 per cent.).

The data of Lichtenheld, in Leipzig, give the frequency with which
various organs were affected, as shown in the following table:--

-----------+---------+-------------------+---------+---------
| Cattle | Pigs | Sheep | Horses
-----------+---------+-------------------+---------+---------
| | ♂ | ♀ | |
|per cent.|per cent.|per cent.|per cent.|per cent.
Lungs | 69·3 | 16·2 | 21·4 | 52·2 | 5·5
Liver | 27·0 | 74·2 | 72·0 | 44·9 | 94·5
Spleen | 2·2 | 3·2 | 2·7 | 2·9 | --
Heart | 0·75 | 3·2 | 1·3 | -- | --
Kidneys | 0·75 | 3·2 | 1·3 | -- | --
Sub- | | | | |
peritoneal| | | | |
tissue | -- | -- | 1·3 | -- | --
-----------+---------+---------+---------+---------+---------

STRUCTURE AND DEVELOPMENT OF ECHINOCOCCUS (HYDATID).

An echinococcus is a spherical or roundish bladder full of a watery liquid, which originates by liquefaction of the oncosphere, and in man may attain the size of a child’s head, but remains smaller in cattle (the size of an orange or apple). The thin wall of the bladder is composed of an external laminated cuticle (ectocyst) and an internal germinal or parenchymatous layer (endocyst). The latter again exhibits two layers: an outer layer of small cells that are less sharply defined, and an inner layer of larger cells. It contains, in addition, calcareous corpuscles, muscular fibres and excretory vessels. It is rich in glycogen.

FIGS. 252 and 252A.--Diagrams of mode of formation of brood capsule and scolices. (1) Wall of mother cyst, consisting of ectocyst and endocyst; (2) theoretical stage of invagination of wall; (3) a brood capsule with the layers of the wall in the reverse position to that in the mother cyst; (4) evagination of wall; (5) invagination; (6) fusion to form the solid scolex; (7) invagination of fore-part of scolex into hind-part. (_Note._--The size of the scolex is much out of proportion to the brood capsule.) (Stephens.)]