Chapter XIII: Appendix: “Rhizopods in Poliomyelitis acuta.” (7)

Although the natural mode of transmission of the Sarcosporidia remains to be determined, yet various experimental researches on the problem are of interest and importance. Theobald Smith (1901) found that mice could be experimentally infected with _S. muris_ by feeding them with the flesh of other infected mice. The incubation period was a long one, namely forty to fifty days. Thus, on the forty-fifth day after feeding young Sarcosporidia were found, and seventy days after feeding spore formation began. Ripe spores were found two and a half to three months after the commencement of these experiments. This mode of infection--a cannibalistic one--hardly seems likely to be the natural method for the infection of sheep and ruminants generally. Smith’s researches have been confirmed. Nègre[225] (1910) found that the fæces of mice fed on infected muscular tissue were infective to other mice when ingested by them. Negri[226] infected guinea-pigs with _S. muris_ by feeding them on infected mouse flesh, and found that the parasite in guinea-pigs showed different characters from those exhibited by it in mice. Darling[227] also succeeded in infecting guinea-pigs with _S. muris_, and Erdmann infected mice with _S. tenella_ (from the sheep).

[225] _C. R. Soc. Biol._, lxviii, p. 997.

[226] _Centralbl. f. Bakt._, Orig., xlvii, p. 612; see also xlvii, p. 56; lv, p. 373.

[227] _Journ. Exptl. Med._, xii, p. 19.

According to Erdmann[228] (1910) the Sarcosporidian spore germinates in the intestine of the host, which has recently ingested infected material. The spore liberates its contained toxin--sarcocystin--which acts upon the adjacent intestinal epithelium, whereby the latter is shed, and an amœbula creeps out of the spore. The amœbula is able to penetrate the denuded area and get directly into the lymph-spaces of the submucous coat of the intestine. The first period of development, lasting some twenty-eight to thirty days, is said to be passed in the lymph-spaces of the intestine. Later the amœbula reaches a muscle fibre. Writing in May, 1914, Erdmann[229] records the appearance of small amœboid and schizogony forms six days after infection of the host. Crawley[230] (1913) controverts some of these statements and considers that the Sarcosporidian spore, still sickle-shaped, bores its way into the epithelial cells of the intestine and comes to rest there. The spore then becomes round or elliptical, and peripheral masses of chromatin appear within it, suggesting schizogony. This happens about twelve hours after feeding, and in twenty-four hours the spores appear to have left the intestine. More recently (May, 1914), Crawley[231] considers that there is sexual differentiation among the Sarcosporidian spores, a few hours after their ingestion by the host.

[228] _Sitz. Gesell. naturf. Freunde zu Berlin_, p. 377.

[229] _Proc. Soc. Exper. Biol. and Med._, xi, p. 152.

[230] _Science_, xxxvii, p. 498.

[231] _Proc. Acad. Nat. Sci._, Philadelphia, May, 1914, p. 432.

Interesting discussions have occurred as to the site of the toxic sarcocystin within the spore. Metachromatic granules occur in the middle of the Sarcosporidian spore (fig. 109), and the toxin may be contained in these grains, as they disappear, according to Erdmann, before the amœbula penetrates the denuded intestinal wall. However, a polar capsule, containing a polar filament, may be present at one end of a Sarcosporidian spore. Laveran and Mesnil described a striated area at the more pointed end of the spore of _S. tenella_, which area they consider to represent a polar capsule. Fantham[232] (1913) found a vacuole-like, polar capsule area in the spores of _S. colii_ from the African mouse-bird. The sarcocystin may be contained in the polar capsule. The nucleus of the spore is generally at the opposite, blunter end.

[232] _Proc. Cambr. Philosoph. Soc._, xvii, p. 221.

Again, various authors have stated that Sarcosporidian spores may occur in the blood of the host at times. If so, then an intermediate host may be concerned in their transmission. Perrin suggested that Sarcosporidia might be spread by blow-flies and flesh-flies.

The classification of the Sarcosporidia as proposed by R. Blanchard, which was based on their various habitats, can no longer hold, because the same species may occur in the muscles as well as in the connective tissue. For the present, the few species that are known may be placed in one genus, _Sarcocystis_, Ray Lankester, 1882.

The following species of _Sarcocystis_ are of interest:--

_S. miescheriana_, Kühn, 1865, in the pig.

_S. bertrami_, Doflein, 1901, in the horse.

_S. tenella_, Railliet, 1886, in sheep. _S. tenella bubali_ in buffaloes in Ceylon and Egypt.

_S. blanchardi_, Doflein, 1901, in cattle.

_S. muris_, Blanchard, 1885, in the mouse, to which it is lethal.

_S. hueti_, Blanchard, 1885, in the seal.

_S. colii_, Fantham, 1913, in the African mouse-bird, _Colius erythromelon_.

Also various Sarcosporidia from antelopes, monkeys, opossum, birds, the gecko and wall-lizard are known.

The spores of _S. muris_, _S. bertrami_, _S. tenella_, and _S. colii_ can multiply by longitudinal fission.

SARCOSPORIDIA OBSERVED IN MAN.

(1) Lindemann[233] found on the valves and in the myocardium of a person who had died of dropsy certain brownish masses, 3 mm. in length and 1·5 mm. in breadth which he regarded as gregarines. If these were actually independent animal organisms it may be suggested that they were Sarcosporidia. Rivolta (1878) named the species _S. lindemanni_.

[233] “Ueb. d. hyg. Bdtg. d. Gregarinen,” _Dtsche. Ztschr. f. Staatsarzneikunde_, 1868, xxvi, p. 326.

(2) Rosenberg[234] found a cyst 5 mm. in length and 2 mm. in breadth in a papillary muscle of the mitral valve of a woman, aged 40, who had died from pleuritis and endocarditis. The cyst contained no scolex nor hooklets of tænia. Numerous small refracting bodies, round, oval or kidney-shaped, were found in a daughter cyst, as well as sickle-shaped bodies. The description hardly appears to indicate Sarcosporidia.

[234] “Ein Befund von Psorosp. in Herzmusk d. Menschen,” _Ztschr. f. Hygiene_, 1892, xi, p. 435.

(3) Kartulis[235] observed Miescher’s cylinders of various sizes in the liver (?) and in the muscular system, of a Sudanese who had succumbed to multiple abscesses of the liver and abdominal muscles. This may be considered as the first actual case of the occurrence of Sarcosporidia in man. Koch in 1887 described a case in Egypt.

[235] Kartulis, “Ueb. pathog. Protoz. b. Menschen,” _Ztschr. f. Hyg. u. Inf._, 1893, xiii, p. 1. Compare also Braun, M., _Die Thier. Par. d. Mensch._, 2nd Edit., Wrzbg., 1895, p. 92; Braun, M., “Z. Vork. d. Sarcosp., b. Menschen,” _Centralbl. f. Bakt._ 1895, xviii, p. 13.

(4) The case reported by Baraban and St. Remy[236] was at once demonstrated as certain. It related to a man who had been executed, and in the laryngeal muscles of whom Sarcosporidia were found; the length of the parasites varied between 150 µ and 1,600 µ, their breadth between 77 µ and 168 µ. The affected muscular fibres were distended to four times their normal thickness. This species was described by Blanchard as “_Miescheria_” _muris_, but according to Vuillemin, it was more probably _Sarcocystis tenella_ of the sheep.

[236] “Sur un cas de Tub. Psorosp. ob. chez l’homme,” _C. R. Soc. Biol._, Paris, 1894 (x), I, p. 201. “Le Parasitisme d. Sarcosp. chez l’homme,” _Bibliogr. Anat._ 1894, p. 79.

(5) Vuillemin has also described a case of Sarcosporidia found in the muscles of a man who died from tubercle at Nancy. The author considered that the parasite corresponded to _S. tenella_.

(6) Darling[237] (1909) found Sarcosporidia in the biceps of a negro from Barbados.

[237] _Arch. Internal Med._, III, p. 183.

The Myxosporidia, Microsporidia, Actinomyxidia and possibly the Sarcosporidia may be included within the section *Cnidosporidia* (Doflein), since they possess spores containing polar capsules.

Order. *Haplosporidia*, Caullery and Mesnil.

The Haplosporidia are a group of organisms having both a simple
structure and life-history. The simplicity may represent a primitive
condition or may be due to degradation resultant on parasitism, and
thus it is possible that the group is not a homogeneous one. The
order Haplosporidia was created by Caullery and Mesnil in 1899, and
includes parasites of rotifers, annelids (fig. 110), crustacea, fish,
prochordates and man. They may be present in the body cavity or
alimentary tract, and can also occur in the septum nasi of man, in
the nervous system of Cephalodiscus, and in tumours of fish.

As the name implies, the spores of the Haplosporidia are simple,
without polar capsules, and are uninucleate. In some genera, _e.g._,
_Haplosporidium_, _Urosporidium_ (fig. 111) there is a spore-coat
or sporocyst which may be elongate or spiny. The developmental
cycle of a Haplosporidian, such as _Haplosporidium_ or _Bertramia_,
begins with a small, uninucleate cell, often rounded, possessing a
cell membrane that may be prolonged into processes. Growth takes
place, coupled with an increase in the number of nuclei, so that a
multinucleate trophozoite is produced. Later, this multinucleate
trophozoite becomes segmented into a number of ovoid or spherical
pansporoblasts, which give rise to few (one to four) spores. Such a
spore, when set free, begins the life cycle over again.

More recently (1905–1907) two important organisms have been
described and included in this group, namely, _Neurosporidium
cephalodisci_[238] (Ridewood and Fantham) from the nervous system
of the prochordate, _Cephalodiscus nigrescens_, and _Rhinosporidium
kinealyi_ (or _seeberi_) from the septum nasi of man. In the case of
_Rhinosporidium_ and _Neurosporidium_, after the uninucleate spore
has grown into a multinucleate trophozoite, the latter segments into
uninucleate pansporoblasts, as in the preceding cases. A difference
then occurs, for each pansporoblast enlarges, its nucleus divides
and a “spore-morula” is formed. Thus a multinucleate pansporoblast
or spore-morula, divided into many uninucleate sporoblasts (spore
mother cells) is produced, and each sporoblast without further change
becomes a uninucleate spore.

[238] _Quart. Journ. Microsc. Sci._, li, p. 81.

The Haplosporidia have therefore been divided by Ridewood and Fantham
(1907)[239] into two sections:--

[239] See Fantham, _Brit. Assoc. Reports_, 1907, p. 553.

(1) The _Polysporulea_, wherein the pansporoblast gives rise to
a number of spores (nine or more), _e.g._, _Rhinosporidium_,
_Neurosporidium_.

(2) The _Oligosporulea_, wherein the pansporoblasts give rise
each to a few (four) spores or to only a single spore, _e.g._,
_Haplosporidium_, _Bertramia_, _Cœlosporidium_, _Ichthyosporidium_.

*Rhinosporidium kinealyi*, Minchin and Fantham, 1905.

_Rhinosporidium kinealyi_, parasitic in man, must now be considered in greater detail. This organism was found in nasal polypus in India, and has since been recorded from the ear as small nodules in the external auditory meatus. The Indian cases came from the neighbourhoods of Calcutta and Madras, and the parasite has been seen in Ceylon. Similar structures have since been described from the United States and South America.

The Rhinosporidium polypus is said not to be particularly painful, though nasal forms must interfere with breathing to some extent. The first nasal polyp reported from India formed a vascular pedunculated growth on the septum nasi and was about the size of a large pea or raspberry. It was compared with a raspberry, being red in colour with a number of small whitish dots upon its surface. When the tumour was cut, a number of similar whitish dots were seen within. These were the cysts of Rhinosporidium. According to Minchin and Fantham[240] (1905), they vary considerably in size and measure up to 200 µ or 250 µ in diameter. Each possesses a cyst wall which varies in thickness in different cysts. Its outer wall is always firm and distinct, the inner limit being less definite at times. Each large cyst is filled with numbers of spherical or oval bodies, showing every gradation between small ones at the periphery and large ones at the centre (fig. 112). Roughly, three zones of parasites can be distinguished in a large cyst, a peripheral set consisting of the youngest parasites, an intermediate group and a central, oldest zone. A large cyst may possess a pore for the egress of its contents. Some of the cysts show polar distribution of the zones.

[240] _Quart. Journ. Microsc. Sci._, xlix, p. 521.

The youngest forms of Rhinosporidium are difficult to detect. They are small, granular masses, round, ovoid or irregular and at times even amœboid in appearance. These are young trophozoites. They increase in size, but encystment occurs early, the outer layer becoming firm so that the organisms have a definite contour. Each is soon multinucleate and the cytoplasm segments around the nuclei. The cyst thus becomes full of uninucleate pansporoblasts or sporonts, with a peripheral layer of undifferentiated protoplasm. The pansporoblasts grow in size. In the larger cysts the formation of pansporoblasts progresses at the expense of the peripheral layer of protoplasm, which, however, continues to grow, so that the cyst as a whole increases in size. The pansporoblasts at first are uninucleate (fig. 112, _a_), and then undergo nuclear multiplication. This is well seen in the intermediate zone of parasites, where the pansporoblasts show first one, then two, then four or more spores (fig. 112, _b_), while in the oldest centrally placed pansporoblasts, about a dozen or sixteen closely packed spores (fig. 112, _c_), can be seen. The spore is small and rounded, and its nucleus is clear and distinct. The fully formed pansporoblast or spore morula becomes surrounded by a membrane.

Certain of the cysts have been found in a ruptured condition, whereby the spores have been liberated into the surrounding tissue. It is almost certain that the spores serve for the auto-infection of the host, for though the tumours of Rhinosporidium seemed to have been removed entirely, it has been found that they recur, some minute fragment of the parasite having probably been left behind. The method whereby the parasite reaches new hosts has not yet been determined, and it would be of interest if its life-history could be more fully investigated.

The Asiatic specimens of _R. kinealyi_ were first described in detail by Minchin and Fantham (1905) from material briefly reported to the Laryngological Society of London in 1903, by O’Kinealy. Material obtained by Dr. Nair, of Madras, was described by Beattie[241] in 1906. This material came from Cochin. Castellani and Chalmers have found similar polypi in Ceylon.

[241] _Journ. Pathol. and Bacteriol._, xi, p. 270; and _Brit. Med. Journ._, Nov. 16, 1907, p. 1402.

Wright[242] has described the parasite from Memphis, Tennessee. Seeber[243] in 1896 described nasal polypi in Buenos Ayres, and in 1900 Wernicke named the parasite therein _Coccidium seeberi_. Seeber’s parasite is a Rhinosporidium, _R. seeberi_, and may ultimately be found to be the same as _R. kinealyi_. Ingram[244] reports Rhinosporidium cysts, with pores in the cyst walls, in conjunctival polypus and in papilloma of the penis in India. Zschokke has reported the presence of _Rhinosporidium_ in horses in South Africa.

[242] _New York Med. Journ._, December 21, 1907, p. 1149.

[243] _La Ciencia Medica_ (Buenos Ayres), 1912.

[244] _Lancet_, September 3, 1910, p. 726.

Class IV. *INFUSORIA*, Ledermüller, 1763.

The Infusoria (or Heterokaryota, Hickson, or Ciliophora, Doflein) include the Ciliata and the Suctoria. A few authorities, including Braun, raise the Suctoria (or Acinetaria) to separate rank as a class, but this is not widely followed.

The body of the Ciliata usually is bilaterally symmetrical and is enveloped in a cuticle which has numerous openings for the protrusion of the cilia. Most kinds have a fixed shape, whilst changes in the form of others are brought about by the contractions of the body substance. The latter exhibits hyaline ectoplasm, in which myonemes, and occasionally also trichocysts (minute spindle-shaped bodies) appear, and granular endoplasm which may contain numerous vacuoles. The cilia, on whose various arrangements the classification is based, are always processes of the ectoplasm. Their form varies; they may be hair-like, or more rarely thorn-like, spur-like, or hook-shaped; undulatory membranes also may occur, which are probably composed of fused cilia.

With the exception of some of the parasitic species, an oral cavity, peristome or cytostome, is always present. It is frequently beset with cilia or provided with undulatory membranes, which help to waft the food inwards; sometimes there is an anal aperture (cytopyge) generally placed at the opposite pole of the organism. A cytopharynx fringed with cilia or sometimes with a specialized supporting apparatus is connected with the peristome. Vacuoles form round the ingested food, and in many species a constant rotation goes on in the endoplasm. Often one, and sometimes two contractile vacuoles are present, the frequency of the pulsations of which depends on the surrounding temperature. Sometimes special conducting channels lead to the vacuoles, or there are outlet channels leading to the exterior.

There is in almost every case a large nucleus (macronucleus), and lying close up to it a small nucleus (micronucleus). The form of the large nucleus varies according to the species. Numerous nuclei are not very common, but these occur in _Opalina_, which lives in the hind-gut of amphibia, and is also distinguished by the absence of an oral aperture.

Reproduction is effected by binary fission; less commonly, after encystment, by multiple division, or by budding. The divisions can be repeated many times, but finally cease, and then the conjugation of two specimens brings about a regeneration, particularly of the nuclei. Numerous examinations (Bütschli, Hertwig, Maupas, Calkins) have demonstrated that after two individuals have associated by homologous parts of the body, the micronucleus separates from the macronucleus, becomes larger and divides twice by mitosis, so that four micronuclei are present in each one of the two individuals forming the couple. Three of these nuclei perish and become absorbed, the fourth gradually passes to the portion of protoplasm connecting the two conjugants, which has originated by absorption of the cuticle at the point of contact of the conjugants. After a further division one micronucleus of each conjugant passes over into the other conjugant, and fusion ensues between the two micronuclei of each individual. Complicated changes and divisions may occur, but only the main principles can be noted here. A new nuclear body is thus formed in each conjugant, and soon divides into two. Of the segments thus produced one becomes a micronucleus, and one or several of the others, as the case may be, form or amalgamate into a new macronucleus, the old macronucleus usually perishing or becoming absorbed during the conjugation. Usually, sooner or later, the two conjugants separate, or may have separated already, and again multiply independently by fission until a series of divisions by simple fission is again followed by conjugation. The theoretical significance of conjugation cannot be dealt with fully here. It may be remarked, however, that the macronucleus plays no part in it, but governs entirely the metabolism of the Infusorian, whereas the micronucleus is essentially a generative nucleus from which macro- and micro-nuclei are again and again produced.

Encystment amongst the Infusoria is very general, and is essentially a means of protection when the surrounding medium dries up. Doubtless these cysts are frequently carried long distances by the wind, which explains the wide geographical distribution of most species. Also, multiplication often takes place in the encysted condition.

Some Infusoria live a free life, others are sedentary; the latter form colonies in fresh as well as in salt water. Numerous species are parasites of various lower and higher animals,[245] and a few also are parasitic in man.

[245] It may be stated that numerous peculiarly shaped species live in the stomach of ruminants, others in the colon of horses. Several species are found in the rectum of frogs and toads; others, again, on the surface of the bodies of fishes; and various other species exist in and on the bodies of invertebrate animals.

The Prague zoologist, v. Stein, introduced a classification of the Infusoria that has been almost universally adopted. It is founded on the different position of the cilia on the body. Though, no doubt, artificial, it is a convenient system. Bütschli has compiled a better one.[246] But for our purpose Stein’s system is sufficient:--

[246] Bronn’s _Cl. u. Ordn. d. Thierr._, i, Protozoa, Part 3, Infusoria.

Order 1. _Holotricha_, Infusoria with cilia that are evenly
distributed over the entire body.

Order 2. _Heterotricha_, ciliated all over like the _Holotricha_, but
having stouter cilia about the peristome.

Order 3. _Hypotricha_, only ciliated on the ventral surface.

Order 4. _Peritricha_, with only a ring of spiral cilia, mostly
sedentary.

The Infusoria observed in man belong to the order _Heterotricha_, with few exceptions.

Genus. *Balantidium*, Claparède et Lachmann.

Heterotrichous Infusoria of oval or bag-like form and almost circular
on transverse section; the anterior extremity narrowed, the posterior
end broad and rounded off, or also narrowed; the peristome starting
at the anterior end is broadest there and becomes narrower as it
gradually obliquely approaches towards the posterior extremity. There
are coarse cilia along the entire left border and the anterior part
of the right border. Longitudinal striation is distinct and regular.
There are two contractile vacuoles on the right, and occasionally
also two or more to the left. The anus (cytopyge) is terminal. The
macronucleus is usually horse-shoe or kidney-shaped, sometimes oval;
the micronucleus contiguous. Reproduction is by binary fission and
conjugation, and encystment occurs. The cysts are spherical or oval.
These ciliates are parasitic in the large intestine of human beings
and pigs, in Amphibia, and in the body cavity of polychæte Annelida.

*Balantidium coli*, Malmsten, 1857.

Syn.: _Paramæcium coli_, Malmsten, 1857.

The body is oval, 60 µ to 100 µ in length (up to 200 µ according to Janowski), and 50 µ to 70 µ in breadth. The peristome is funnel-shaped or contracted, the anterior end being then broadened or pointed according to the degree of contraction (figs. 113, 114). The ecto- and endo-plasm are distinct, the latter is granular, containing drops of fat and mucus, granules of starch, bacteria, and occasionally also red and white blood corpuscles. There are usually two contractile vacuoles, seldom more. The anus (cytopyge) opens at the posterior extremity. The macronucleus is bean- or kidney-shaped, rarely oval; the micronucleus is spherical.

_Balantidium coli_ lives in the large intestine of man, in the rectum of the domestic pig, and has been found in monkeys. It propagates by transverse division, but conjugation and encystment are known to take place.[247] Transmission to other hosts is effected by the cysts of the parasite (fig. 114).

[247] According to Gourvitch (“Bal. coli. Darmk. d. Menschen,” _Russ. Arch. f. Path., klin. med. u. Bact._, Petrograd, 1896), the conjugated Balantidia are supposed to fuse with each other and form oval cysts two or three times the size of the free organisms, and to divide into numerous globules within the cystic membrane; the process, however, has hitherto not been confirmed. The supposed Balantidium cysts appeared in two patients who were simultaneously suffering from _Dibothriocephalus latus_, after the administration of anthelminthics. It therefore seems, according to the description, that in reality these forms were actually abnormally large, possibly swollen, young eggs of the tape-worm mentioned.

_Balantidium coli_, first seen by Leeuwenhoek, was described by Malmsten in 1857 in a man aged 35 years, who had two years previously suffered from cholera, and since then had been subject to diarrhœa. The examination showed an ulcer in the rectum above the mid sphincter ani, in the sanguineous purulent secretion of which numerous Balantidia were swimming about. Although the ulcer was made to heal, the diarrhœa did not cease and the stools contained numerous Balantidia, the number of which could only be decreased by extensive enemas of hydrochloric acid.

The second case related to a woman who was suffering from severe colitis, and who died ten days after admission. The malodorous, watery evacuations contained innumerable Balantidia, in addition to pus, and at the autopsy the anterior portion of the large intestine was found to be infested with them.

Subsequently this parasite has often been observed in human beings, and various cases have been recorded. These occurred in Russia, Scandinavia, Finland, Cochin China, Italy, Germany, Serbia, Sunda Islands, Philippine Islands, China, and in other parts of Asia and in America. Other cases were reported by Askanazy, Ehrnroth, Klimenko, Nagel, Koslowsky, Kossler, Waljeff, Strong and Musgrave, Glaessner[248] and others. Sievers found _B. coli_ very common in Finland.

[248] _Centralbl. f. Bakt._, Orig., xlvii, p. 351.

In the majority of the cases described by Sievers from Finland, and in other cases from Central Europe, the patients suffered from obstinate intestinal catarrh, which did not always cease even after the Balantidia had disappeared. On the other hand, Balantidia have occasionally still been found to persist, though in small numbers, after the catarrh has been cured. Some authors, nevertheless, do not regard Balantidia as the primary cause of the various diseases of the large intestine, which often commence with the development of ulcers, but they consider that they may aggravate these diseases and render them obstinate. According to Solowjew, Askanazy, Klimenko and Strong and Musgrave, however, the parasites penetrate the intestinal wall, and give rise to ulcerations which may extend deeply into the submucosa, and even be found in the blood and lymphatic vessels of the intestinal wall. According to Stokvis, _B. coli_ occurs also in the lung; at all events this author states that he found one living and several dead paramæcia (?) in the sputum of a soldier, returned from the Sunda Islands, who was suffering from a pulmonary abscess. Sievers has shown that _B. coli_ might occur in persons not suffering from intestinal complaints, but E. L. Walker[249] (1913) states that every person parasitised with _B. coli_ is liable sooner or later to develop balantidian dysentery.

[249] _Philip. Jl. Sc._, Sec. B, viii, p. 333.

Since Leuckart confirmed the frequent presence of _B. coli_ in the rectum of pigs, and corresponding observations were made in other countries, the pig is universally considered to be the means of the transmission of Balantidium to man. The encysted stages only serve for transmission, because, according to all observations, the free parasites have a very small power of resistance. They perish when the fæces have become cool; they cannot live in ordinary, slimy, or salt water. As they are killed by acids even when much diluted, they cannot pass through the normal stomach alive except under the most unusual circumstances. The pigs, in whose intestines the Balantidium appears to cause little or no disturbance, evacuate numerous encysted Balantidia with the fæces, and their occasional transference to man brings about their colonization there, but perhaps only when a disease of the colon already exists.

Experimental transmission of the free parasites to animals (per os or per anum) yielded negative results, even in the case of pigs. Casagrandi and Barbagallo (1896), however, had positive, as well as negative, results. They employed healthy young cats, or cats in which catarrhal entero-colitis had been artificially induced (which in other experiments is apt to cause the death of the animals experimented upon in about six or seven days), or finally cats that had dilatation of the rectum with alkaline reaction of the fæces. An attempt to infect three healthy cats by injecting human fæces containing Balantidium into the rectum proved negative, in so far as the fæces of the experimental animals had an acid reaction and contained no Balantidia, but at the autopsy performed eight days after infection a few encysted parasites were found in the mucus of the ileum. In the case of four cats suffering from entero-colitis, into which human fæces containing Balantidia were introduced per os, Balantidium cysts were found in the fæces three days after the last ingestion. Great numbers, moreover, were found in the cæcum and the posterior part of the small intestine at the autopsy of the animals, which died about eight days after the commencement of the experiments. Actual colonization, therefore, was not effected in either series of experiments. Free or encysted Balantidia of pigs were used for further experiments. The experiments proved negative when fæces containing cysts were injected into the rectum of healthy cats (three experiments), or cats (two) suffering from spontaneous intestinal catarrh, or when such material was introduced per os into three healthy cats. In the case of two cats with intestinal catarrh artificially produced, a small number of the active Balantidia injected into the rectum remained alive. Larger quantities of fæces containing encysted Balantidia were introduced into two other cats affected with the same complaint. These, certainly, did not appear in the fæces, but small numbers, free and alive, were found in the cæcum. Similarly, encysted Balantidia were introduced into two cats with dilated rectum, and whose fæces had an alkaline reaction. In these cases no parasites appeared in the fæces, but three and five days later, when the two animals were examined, a very small number were discovered free in the large intestine. Klimenko did not succeed in infection experiments with _B. coli_ on young dogs, whose intestines had been artificially affected by disease.

More recent experiments by Brumpt have shown that young sucking pigs can be infected with Balantidium from infected monkeys (_Macacus cynomolgus_) and suffer heavily from the same, whereas the Balantidium of the pig is rarely harmful to its host. This and previous experiments may be thought to suggest that there are perhaps several pathogenic species, and also that harmless strains of Balantidium may occur. At the same time, it must be remembered that a large proportion of the cases recorded of Balantidian colitis occur among swineherds and butchers, that is, among people in frequent contact with pigs. Morphologically, there are practically no differences between the Balantidia found in man, monkeys and pigs, and it is probable that one species only, under slightly different environmental conditions, may be responsible for the colitis observed. In any case, efficient prophylactic measures should be taken against balantidiasis in countries where it may occur, by confining the pigs and not allowing them to run in yards and dwellings.

E. L. Walker (1913) has given a good summary of work on balantidiasis. His own researches in the Philippines showed that monkeys could be infected by Balantidia both from pigs and men. Parasites may appear in the stools only at infrequent intervals. He believes that the ciliates are the primary etiologic factor in the symptoms and lesions of balantidian dysentery.

Behrenroth (1913) has given an interesting account of _Balantidium coli_ and its pathogenic significance.

*Balantidium minutum*, Schaudinn, 1899.

The body is of oval form, with the anterior extremity pointed, and posterior extremity broad and rounded (fig. 115). The length is 20 µ to 32 µ, and the breadth is 14 µ to 20 µ. The peristome, which is fissure-like, extends to the centre of the body (fig. 115). The right lateral border of the peristome is beset with cilia the same length as those of the body, the left side terminates in a thin hyaline membrane that extends towards the back, and can pass over to the right side. A row of longer and stronger cilia (cirri) are on the left border of the peristome. The cuticle is refractile, the ectoplasm hyaline and the endoplasm granular, with numerous food vacuoles.

A single contractile vacuole lies dorsally and to one side at the posterior extremity. The macronucleus, which is always spherical, is central and is 6 µ to 7 µ in diameter. The micronucleus, close in front of it, only measures 1 µ (fig. 115). The cysts are oval.

These parasites were found in numbers in the evacuations of a man aged 30, who was born in Germany and had repeatedly travelled between Hamburg and North America, where he made long stays. The patient came to the Charité in Berlin to seek advice for constipation alternating with diarrhœa accompanied by abdominal pain.

A second case (the parasite of which was described as _Colpoda cucullus_ by Schulz) was observed in a patient in the same institution.

As, in both cases, the parasites only appeared during the diarrhœa, and disappeared as soon as the fæces had assumed a normal consistency, or could only be demonstrated in a few encysted specimens, it may be assumed that the small intestine or the duodenum is their habitat.

Genus. *Nyctotherus*, Leidy, 1849.

Flat, heterotrichous Infusoria, kidney- or bean-shaped. The peristome
commences at the anterior pole of the body and extends along the
concave side to the middle, where the oral aperture is situated. The
cytopharynx is oblique and is more or less curved. The cytopyge is at
the posterior extremity, where a single contractile vacuole is also
situated. The macronucleus is almost in the centre of the parasite.
The members of this genus live parasitically in the intestine of
amphibia, insects and myriapods, and at least one species is found in
man.

*Nyctotherus faba*, Schaudinn, 1899.

The body is bean-shaped, and a little flattened dorso-ventrally. It is 26 µ to 28 µ long, 16 µ to 18 µ broad, and 10 µ to 12 µ thick (fig. 116). The peristome is on the right border and extends to the middle; at the left there are large adoral cilia, the cilia on the right border not being larger than those on the body. The cytopharynx is short, slightly curved and turned backwards. The contractile vacuole is large, spherical, situated at the posterior extremity, and its contents are voided through the anus at its left. The macronucleus is in the centre of the body; it is globular (6 µ to 7 µ in size), and contains four or five chromatin masses. The micronucleus lies close to it, and is spherical or somewhat elongate measuring 1 µ to 1·5 µ (fig. 116). The cysts are oval.

This species has hitherto only been seen once in the same patient in whom _Balantidium minutum_ was discovered.

*Nyctotherus giganteus*, P. Krause, 1906.

Under the name _Balantidium giganteum_ n. sp., P. Krause described an Infusorian which was repeatedly observed with _Trichomonas intestinalis_ in the alkaline evacuations of a typhoid patient in Breslau. The body is ovoid, narrower and rounded anteriorly and broader and stunted posteriorly. The peristome lies to one side; the macronucleus is bean-shaped, the micronucleus small and globular; one or two vacuoles are present. The anus is at the farther end. The organism is 90 µ to 400 µ long, 60 µ to 150 µ broad (fig. 117). After a prolonged stay outside the body, it becomes rounded and encystment occurs. In the thermostat the Infusoria remain alive at 37° C. for five weeks.

The species, however, hardly belongs to _Balantidium_, but to all appearances is a _Nyctotherus_ and is distinguished from _N. faba_ by the difference in size.

[*Nyctotherus*] *africanus*, Castellani, 1905.

In the fæces of a native of Uganda who suffered from sleeping sickness and diarrhœa and had in his intestine _Ascaris lumbricoides_, _Trichocephalus trichiurus_ and _Ancylostoma duodenale_, Castellani found a curiously shaped Infusorian, 40 µ to 50 µ long, and 35 µ to 40 µ broad, with spherical macro- and micronucleus and a contractile vacuole (fig. 118). He included the organism in the genus _Nyctotherus_, perhaps wrongly, or the parasite may have been deformed. After the patient’s death the same parasite was found in the intestine and especially in the cæcum.

G. Lindner, in Cassel, studied certain peritrichal Infusoria
(stalkless Vorticella), and connected them, probably incorrectly,
with the most varied diseases of man and domestic animals, even
with Sarcosporidia of pigs. It may be mentioned that according to a
communication by letter from Schaudinn, Vorticella may be found in
freshly evacuated fæces, but always only after the administration of
a water enema. In spite of this, several other investigators mention
Vorticellæ as intestinal parasites of man.

The _Chilodon dentatus_ (Ehrenberg) recorded in 1903 by J. Guiart as
a parasite of man, which may be found in all infusions, can hardly
have lived in the man from whose fæces it was cultivated, but may
represent a chance admixture both in the fæces and the cultivations.
_C. uncinatus_ was also found as a chance parasite of man by Manson
and Sambon. According to Doflein[250] (1911) certain Chilodon-like
organisms have been found by Selenew in prostate secretions in
gonorrhœa. Other species of the genus _Chilodon_ are known, but only
as ectoparasites (_e.g._, _Chilodon cyprini_, Moroff, 1902, from the
skin and gills of diseased carp).

[250] _Lehrbuch der Protozoenkunde_, 3rd ed., p. 963.

A number of other parasitic Ciliates are known, among which
_Ichthyophthirius multifiliis_, destructive to fish, is important. It
lives in the skin and the layers immediately below it, forming small
whitish pustules which may become confluent. The pustules are most
common on the head and fins, but occur also on the eyes and gills of
the host. The young parasite, which is one of many formed in a cyst,
is very small. At first it is free swimming, but soon attaches itself
to the skin of a fish. It bores inwards and becomes surrounded by the
irritated skin. There it attains a relatively large size, being 500 µ
to 750 µ and occasionally more in diameter. The body has a rounded
terminal mouth, short cytopharynx and a number of minute contractile
vacuoles. The macronucleus is large and horseshoe-shaped; the small
micronucleus is only seen in the very young animal. When full grown,
the organism encysts and forces its way to the surface and bursts
through, leaving a small, gaping wound behind. The cyst sinks to the
bottom of the water, nuclear multiplication occurs and a number of
young parasites are produced, which leave the cyst and either attack
new hosts or else perish.

_Opalina ranarum_, parasitic in the rectum and urinary bladder of
frogs and toads, shows great degradation and simplification due
to parasitism, possessing no separate micronuclei, no cytostome,
cytopharynx or cytopyge. It has many macronuclei, and is a large
parasite. During summer and autumn nuclear multiplication followed
by division of the body occurs, the process being repeated after the
daughter forms have grown to the size of their parent. In spring, the
Opalina divide rapidly, but do not grow much before dividing again.
Finally, tiny forms, containing three to six nuclei, encyst and pass
from the host with the fæces. As these latter are greedily devoured
by tadpoles, the _Opalina_ gain new hosts in which they develop.

THE CHLAMYDOZOA.

The name Chlamydozoa was proposed by Prowazek in 1907 for a number of minute, problematic organisms (fig. 119) believed to be the causal agents of certain diseases in man and animals, such as vaccinia and variola, trachoma, inclusion blenorrhœa in infants, molluscum contagiosum, and bird epithelioma contagiosum. Other diseases possibly due to Chlamydozoa[251] are hydrophobia, measles, scarlet fever, foot-and-mouth disease, the “Gelbsucht” disease of silkworms, and perhaps even typhus (Prowazek, 1913). The subject is difficult and controversial and can only be briefly discussed here. It is known that the viruses in all these diseases can pass through ordinary bacterial filters, that is, they belong to the group of “filterable viruses.” At such periods the organisms are extracellular or free. It is also known that in many of these cases the virus produces definite and characteristic reaction-products or cell-inclusions in the infected cells, during the intracellular phase of the life-history of the organism. As the organisms to be considered are problematic, it will be convenient to summarize their history:--

[251] For a detailed account of the Chlamydozoa see Prowazek’s _Handbuch der Pathogenen Protozoen_, Bd. i (1911–12). Leipzig, J. A. Barth.

(1) Cell-inclusions, usually named after their discoverers, have been found in certain diseases, thus: In vaccinia Guarnieri’s bodies, in scarlet fever Mallory’s bodies, in hydrophobia Negri’s bodies, in trachoma Prowazek’s bodies occur.

(2) At first these characteristic cell-inclusions were considered to be actual parasitic organisms causing the diseases in question. The bodies received zoological names and attempts were made to work out their supposed development cycles. The supposed parasites of vaccinia and variola were referred to a so-called genus _Cytoryctes_, those of hydrophobia to _Neuroryctes_, of scarlet fever to _Cyclasterium_, while those of molluscum contagiosum were referred to the Coccidia. Calkins in 1904 studied in detail the cell-inclusions of vaccinia and small-pox, calling them _Cytoryctes variolæ_, Guarnieri. Calkins considered that in the stratified cells of the epidermis they passed through two cycles, the one cytoplasmic, the other intranuclear. The first is the vaccinia cycle, the second the pathogenic (intranuclear) variola cycle. It is hardly necessary to follow all Calkins’ stages here.

Negri (1909) described a cycle for _Neuroryctes hydrophobiæ_. Calkins refers both _Cytoryctes variolæ_ and _Neuroryctes hydrophobiæ_ to the Rhizopoda.

Siegel (1905) described quite different organisms under the name _Cytorhyctes_. He listed several species: _C. vacciniæ_; of vaccinia and small-pox, _C. scarlatinæ_ of scarlet fever, _C. luis_ of syphilis (this is probably the granule stage of _Treponema pallidum_), and _C. aphtharum_ of foot-and-mouth disease.

(3) The afore-mentioned views were criticized, and the bodies were not considered to be living organisms but merely reaction products or cell-inclusions due to the effects of the virus on the host cells. Thus Guarnieri’s bodies were stated to consist of extruded nucleolar or plastin material, having no developmental cycle. It was further asserted that infection could be produced by lymph in which Guarnieri’s bodies had been destroyed. Similar assertions have been made regarding the Negri bodies, and others. The _Cytoryctes_, _Neuroryctes_, etc., are considered, according to these views, to be degeneration products of the nucleus or to be of a mucoid nature.

(4) More recently a positive belief has gained ground that there are true parasitic organisms causing these diseases, and that the parasites are very minute, being termed Chlamydozoa by Prowazek and Strongyloplasmata by Lipschütz.

The Chlamydozoa are characterized by (_a_) their very minute size, smaller than any bacteria, so that they can pass through bacterial filters; (_b_) they pass through intracellular stages, in the cytoplasm or the nucleus of the host cell, producing therein the reaction products or inclusions in the cell already recorded as characteristic or diagnostic of the diseases produced; (_c_) they pass through definite developmental cycles. Such a cycle consists essentially of growth and division. The mode of division of the Chlamydozoa resembles that of the centriole of a cell, by the formation of a dumb-bell-shaped figure. Two dots are observed connected by a fine line or strand which becomes drawn out and finally snaps across the middle. Prowazek and Aragão (1909) working on smallpox in Rio de Janeiro found that the chlamydozoal granules passed through a Berkefeld filter and that the filtrate was virulent. But if an “ultra-filter” were used, _i.e._, one coated with agar, then the granules were retained and the filtrate was no longer virulent. The surface of the ultra-filter was found to contain many granules.

The Chlamydozoa are parasites of epiblastic tissues (_e.g._, epidermal cells, nerve cells, conjunctival cells).

The life-history of a Chlamydozoön (fig. 119), such as that of vaccinia, is, according to Prowazek, Hartmann and their school, as follows:--

1. The infection begins with _elementary bodies_ or _elementary corpuscles_ which live at first extracellularly. An elementary body is a minute speck of chromatin, apparently devoid of cytoplasm, which can pass through a bacterial filter. It can enter a host cell, but the entry is not a process of phagocytosis.

2. Inside the host cell the elementary body grows in size, and becomes an _initial body_ (fig. 119, _a_).

3. A reaction on the part of the host cell results, for nucleolar, plastin substance is extruded from the cell-nucleus and surrounds the parasitic initial body. The latter is thus enveloped in a mantle (hence the name Chlamydozoa, from χλαμὑς, a mantle), and the characteristic cell-inclusion (Guarnieri’s body, Negri’s body, etc.) is produced. The nucleolar, mantle substance probably represents the “cytoplasm” of _Cytoryctes_, described by Calkins.

4. The body next breaks up into a number of smaller bodies known as _initial corpuscles_. These, in their turn, divide by simple division (in the manner already described) into numerous elementary bodies (fig. 119). Thus, the life-cycle is completed.

The Chlamydozoa are, then, the minute granules inside the body of the _Cytoryctes variolæ_ or the _Neuroryctes hydrophobiæ_, so that the whole body of the _Cytoryctes_ or _Neuroryctes_ corresponds to the mantle and parasite of the Chlamydozoön. The Cytoryctes group is said to cause destruction of the host cell. The Cytoöikon group (_e.g._, trachoma bodies) causes proliferation of the host cell.

In September, 1913, Noguchi[252] described the cultivation of the parasite of rabies in an artificial medium, similar to that used by him for the cultivation of _Spirochæta recurrentis_. The cultures were stated to be infective to dogs, rabbits and guinea-pigs. Levaditi, in December, 1913, stated that he had succeeded in cultivating spinal ganglia of rabid monkeys in monkey plasma.

[252] _Journ. Exptl. Med._, xviii, p. 314.

Noguchi and Cohen (November, 1913)[253] have succeeded in cultivating the so-called trachoma bodies, or at any rate bodies very closely resembling them morphologically. The medium employed was Noguchi’s ascitic fluid and rabbit kidney medium, as used for spirochætes. The coarser cultural forms stained blue with Giemsa’s solution, the finer ones stained red. Attempts to infect monkeys from the culture tubes failed.

[253] _Idem_, p. 572.

From their behaviour on treatment with such reagents as saponin, bile and sodium taurocholate, Prowazek considers that the Chlamydozoa approach the Protozoa.

* * * * *

PROTOZOA INCERTÆ SEDIS.

*Sergentella hominis*, Brumpt, 1910.

Et. and Ed. Sergent in 1908 found vermiform bodies about 40 µ long by 1 µ to 1·5 µ broad in the blood of an Algerian suffering from nausea and cold sweats, without other symptoms. The bodies were pointed at each end, with a somewhat ill-defined nucleus in the middle. Their systematic position is doubtful.

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|NOTE.--An Appendix on Protozoology will be found on pp. 733–752. |
|This has been prepared in order to incorporate a number of new |
|additions to knowledge made since the body of the book was |
|printed off. |
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B. *PLATYHELMINTHES*, or Flat Worms.

BY

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

DEFINITION: Bilaterally symmetrical animals without limbs, the form
of which is leaf or tape-like, rarely cylindrical, and whose primary
body cavity (segmentation cavity) is absent, the cavity being filled
by a mesenchymatous tissue (parenchyma).

The mouth is either situated at the anterior end of the body, or is
shifted more or less backwards on to the flat ventral surface. The
alimentary canal consists of a short fore-gut, which is frequently
provided with a muscular pharynx, and of a simple forked or branched
mid-gut; there is neither a hind-gut nor an anus; in one class, the
Cestodes, the alimentary canal has entirely disappeared except for
muscular remnants in the scolex.

The INTEGUMENT OF THE BODY consists either of a ciliated epithelium
of only one layer (Turbellaria), or of a cuticle and gland-like
cells embedded in the parenchyma, or subcuticular layer (Cestodes,
Trematodes). The dermo-muscular layer consists of annular,
longitudinal, and even diagonal fibres, while the parenchyma is
traversed by dorso-ventral fibres.

The central NERVOUS SYSTEM, which is embedded in the parenchyma of
the body, consists of cerebral ganglia, united together in the shape
of dumb-bells, and of two or more longitudinal MEDULLARY FASCICLES,
often forming transverse anastomoses. Organs of sense usually occur
only in the free-living species, more rarely during the free-living
stages of a few parasitic species and in a few ectoparasitic forms.

[In Platyhelminthes simple eye-spots frequently occur, and in a few
an auditory vesicle.]

BLOOD-VESSELS and definite RESPIRATORY ORGANS are lacking [except
in _Nemertinea_]; the EXCRETORY APPARATUS (formerly termed
water-vascular system) is typical of the entire class. It commences
in the interstices of the parenchyma, with peculiar terminal cells
(ciliated funnels), which will be described later (p. 219), the
capillary processes of which go on uniting into larger branches,
and finally form two large collecting vessels, which, sometimes
separately and sometimes united, open to the exterior through one,
two, or numerous pores.

Nearly all the Platyhelminthes are HERMAPHRODITIC, and in nearly all
there are, in addition to the ovaries producing ova, other glands
attached to the female genital apparatus, namely, the vitellaria or
yolk glands, which provide a substance termed yolk, which serves
as nourishment for the embryo. The fully formed eggs have shells
and are “compound,” _i.e._, composed of the egg or ovarian cell,
which is surrounded by numerous yolk cells or their products of
disintegration. The two sexual openings usually lie close together,
frequently in the fundus of a genital atrium; they are rarely
separated from one another. Shell glands also usually occur (p. 221).

Reproduction is sexual, often, however, combined with asexual methods
of propagation (segmentation, budding). The Platyhelminthes live
partly free in fresh or salt water, exceptionally also on land. The
greater part, however, live as parasites on or in animals.

CLASSIFICATION OF THE PLATYHELMINTHES.

_Class I._--*Turbellaria* (or Eddy Worms). Flat worms for the most
part, free living, and always covered with a ciliated epithelium.

_Order 1._--_Rhabdocœlida_, gut unbranched.

_Order 2._--_Tricladida_, gut with three main branches.

_Order 3._--_Polycladida_, a central gut with lateral cæca.
Development direct or through metamorphosis. They live in fresh and
salt water or on land; very seldom as parasites.

_Class II._--*Trematoda* (Sucking Worms[254]). [Usually known as
Flukes.--F. V. T.] Flat worms, living as ecto- or endoparasites, that
are only ciliated in the larval condition, and in their adult state
are covered with a cuticle, the matrix cells of which lie in the
parenchyma. They have either one, a few, or several suckers,[255] and
frequently also possess chitinous fixation and adhesive organs. The
intestine is single, but generally bifurcated, and not uncommonly there
are transverse anastomoses between the forks or diverticula on them.
Excretory organs double, with two orifices at the anterior extremity
or a single one at the posterior end. Development takes place by a
metamorphosis or alternation of generations (p. 283). These worms are
almost always hermaphroditic, with two or more female and one male
sexual orifice. They live, almost without exception, as parasites on
vertebrate animals, but the intermediate generations are passed in
molluscs.

[254] This grouping goes back to the year 1800, and was made by J. G. H. Zeder, a physician and helminthologist of Forchheim, who divided the helminths, which until 1851 were generally regarded as a special class of animals, into the groups of round, hook, sucker, tape and bladder worms, as which they are recognized up to the present time. In 1809, K. A. Rudolphi gave them the names _Nematodes_, _Acanthocephali_, _Trematodes_, _Cestodes_ and _Cystici_.

[255] A sucker or acetabulum (little cup) is a round, cup-shaped muscular organ, the muscles of which are _sharply defined_ from those of the body.

_Class III._--*Cestoda* (Tapeworms). Endoparasitic flat worms without
an alimentary canal. The larval stages are rarely ciliated, but are
usually provided with six spines; the adult worm is covered with a
cuticle, the matrix cells of which are embedded in the parenchyma. The
body consists of a single segment (Cestodaria) or a chain of segments,
in which case it consists of the scolex and the segments containing
the sexual organs (proglottides) (Cestodes s. str.). The scolex is
provided with various adhesive and fixation organs, and there are
calcareous corpuscles in the parenchyma. Excretory organs symmetrical,
opening at the posterior end. These worms are always hermaphroditic,
and then possess one or two female and one male sexual orifice. During
development a larval intermediate stage (“measle”) occurs and almost
always in a different host to that in which the adult sexual worm
lives. The adult stage is parasitic in vertebrate animals; but the
larval stage may occur in invertebrates.

Class II. *TREMATODA*, Rud.

These worms are usually leaf- or tongue-shaped, but also barrel-shaped or conical; they vary from 0·1 mm. to almost 1 m.[256] in length; most of them, however, are small (5 mm. to 15 mm.). The surface on which the orifice of the uterus and the male sexual opening are situated is termed the ventral surface; the oral aperture, which also acts as anus, is always at the anterior end in the sub-order _Prostomata_ (p. 230), but in the sub-order _Gasterostomata_ it is ventral.

[256] _Nematobothrium filarina_, van Bened., on the branchial chamber of the Tunny.

Suckers are always present and occur in varying numbers and positions at the anterior extremities as well as on the ventral surface, and occasionally on the lateral margin and on the dorsum; the beginning of the intestine (mouth) is always surrounded by a sucker in the _Prostomata_.

In or near the suckers there may be chitinous hooks, claws or claspers, or the surface of the body is more or less covered with spines, scales or prickles; in one genus (_Rhopalias_) there are projectile tentacles beset with spines on the sides of the anterior part of the body.

The body of adult Trematodes is covered by a homogeneous layer of varying thickness, which either lies directly over the external layer (basement membrane) of the parenchyma, or over the muscles embedded in the parenchyma. This investing membrane (cuticle) arises from pear-shaped or spindle-shaped cells arranged singly or in groups (which lie between or internal to the diagonal muscles), and is connected with them by processes; these cells one may regard as epithelial cells which have sunk down, or possibly as parenchymatous cells. An epithelium of one layer is also found on the body of young stages, but it disappears during growth, and only occasionally do its nuclei persist until adult life. In its place we then find the cuticle, which, moreover, extends into all the body openings more or less deeply.

It is thus a debatable point whether the “investing layer” of flukes is a cuticle--that is, consists of modified epithelial cells--or whether it is a basement membrane, _i.e._, compressed and modified connective tissue cells; in this latter case the true epidermis and cuticle have been cast off. In the former case the epidermal cells are the pear-shaped cells referred to above. According to recent authors it consists of two parts, an outer true cuticle and an inner basement membrane. There are also unicellular cuticular glands, lying isolated or in groups, which are termed cephalic, abdominal, or dorsal glands according to the position of their orifice.