Chapter X: Appendix: “Rhizopods in Poliomyelitis acuta.” (4)

When the ticks were incubated at 21° to 24° C. no spirochætes, as such, were seen in the organs, except perhaps in the gut, where they often disappeared in a few days. When the ticks were previously incubated at 35° to 37° C. for two to three days, spirochætes, as such, reappear in the gut, organs and hæmocœlic fluid. The infection proceeds, not from the salivary gland, but from the infective excrement, that is, from the thick, white material voided by the tick while feeding, usually towards the end of the meal. This Malpighian excrement passes into the wound caused by the bite, being greatly aided by the clear and more limpid coxa fluid, which bathes the under surface of the tick’s body, and mixes with and carries the infective excrement into the wound. Ticks remain infective for a long time.

The spirochætes in the gut of infected ticks divide by a process of multiple transverse fission into granules, which are composed of chromatin (fig. 54). These granules--sometimes known as coccoid bodies--are capable of multiplication. Leishman first found them in clumps inside the cells of the Malpighian tubules (_cf._ fig. 55).

To summarize, when spirochætes are ingested by a tick, some of them pass through the gut-wall into the hæmocœlic (body) fluid. They then bore their way into the cells of various organs (fig. 55_a_) and break up into coccoid bodies. In this manner the granules find their way into the ovaries and ova, thus explaining how the young ticks are born infected. Inoculation of these chromatinic granules usually produces infection. Infective granules are also seen in the rudiments of the Malpighian tubules of embryo ticks. Bosanquet and Fantham (1911), independently, have shown that molluscan spirochætes also break up into similar granules or coccoid bodies. Gross has also demonstrated multiple transverse fission in molluscan forms. Marchoux and Couvy (1913) and Wolbach (1914) consider the granules or coccoid bodies to be degeneration products. This is unlikely (see below).

Schuberg and Manteufel have found that certain _O. moubata_, perhaps 30 per cent. of the specimens of a given neighbourhood, may acquire a natural active immunity against infection with _S. duttoni_.

_S. duttoni_, or a closely allied form (by some termed _S. novyi_), occurs in Colombia, and is spread by the tick _Ornithodorus turicata_. In Panama a similar spirochæte is probably spread by _O. talaje_.

*Spirochæta gallinarum*, Stephens and Christophers, 1905 (= *Spirochæta marchouxi*, Nuttall, 1905).

This Spirochæte, which occurs in fowls and is pathogenic, is transmitted by the tick _Argas persicus_. It is about 10 µ to 20 µ long. There is a pathogenic spirochæte known to occur in geese, named by Sakharoff (1891) _S. anserina_, and found in Caucasia. This may be the same as _S. gallinarum_, in which case the name _S. anserina_ will have priority. These organisms cause fever, diarrhœa, anæmia and death. The life history of the avian pathogenic spirochætes has been studied by Balfour, by Hindle[150] and by Fantham.[151] It is essentially similar to that of _S. duttoni_.

[150] _Parasitology_, iv, p. 463.

[151] _Annals Trop. Med. and Parasitol._ (1911), v, p. 479.

Marchoux and Couvy[152] (1913) consider that the “fragmentation of the chromatin” in spirochætes is a process of degeneration. Working with _A. persicus_ and _S. gallinarum_, they state that a large number of the spirochætes ingested by the Argas almost immediately pass through the wall of the alimentary canal and appear in the hæmocœlic fluid. Marchoux and Couvy consider that Leishman’s granules may be found in the Malpighian tubules of various Arachnids. They found spirochætes in the cephalic glands of infected Argas. They consider that spirochætes remain as wavy spirochætes within the tick, if they are to be infective, though the spirochætes may become so thin as to be invisible! The latter argument is obviously weak, and it was never asserted that all granules in the Malpighian tubules of infected ticks were derived from spirochætes. With dark-ground illumination small, refractile spirochætal granules may be seen to grow into spirochætes. The granule phase of spirochætes has recently been discussed by Fantham[153] (1914).

[152] _Annales Inst. Pasteur_, xxvii, pp. 450, 620.

[153] _Annals Trop. Med. and Parasitol._, viii, p. 471.

*Spirochæta recurrentis*, Lebert, 1874.

Syn.: _Spirochæta obermeieri_, Cohn, 1875.

This organism was discovered by Obermeier (1873) in cases of relapsing fever in Berlin. Short forms 7 µ to 9 µ long, and longer (probably adult) forms, 16 µ to 19 µ, are found in the blood. The width is 0·25 µ. Parasites 12 µ or 13 µ long are often observed.

The spirochæte is found in the blood during febrile attacks and relapses, but not during intervening periods. It can be inoculated into monkeys, rats and mice. It can live in the bed-bug, _Cimex lectularius_, and Nuttall has succeeded in transmitting _S. recurrentis_ from mouse to mouse by the bites of the same bug. The French investigators Sergent and Foley (1908–9) in Algeria, and Nicolle, Blaizot and Conseil (1912) in Tunis, have shown experimentally that _S. recurrentis_ (var. _berbera_) is transmitted by lice. The latter workers also demonstrated the method of infection that commonly occurs, namely, by the scratching of the skin and crushing of lice containing spirochætes on the excoriated surface of the body.

Lice as transmitting agents for relapsing fever were indicated
by Mackie[154] in 1907. An epidemic among Indian school children
furnished the materials.[155] It was noted that out of 170 boys, 137
were infected, and the boys were very verminous. Among the girls, 35
out of 114 suffered, and few lice were found on them. Twenty-four
per cent. of the lice taken from the boys contained spirochætes as
compared with 3 per cent. of those from the girls. As the epidemic
died out among the boys, the lice also became fewer, and an increase
in the number of cases among the girls coincided with an increase in
the number of lice. Spirochætes were found in the gut, Malpighian
tubules and genital organs of the lice. Mackie thought that infection
of the patients was brought about by the regurgitation of the
spirochætes when the lice fed, but proof of this was lacking.

[154] _Brit. Med. Journ._, Dec. 14, 1907, p. 1706.

[155] See also Nuttall, Herter Lecture on Spirochætosis, _Parasitology_, v, p. 269.

In 1912, Nicolle, Blaizot and Conseil,[156] working in Tunis and using chiefly an Algerian strain of relapsing fever spirochætes (sometimes called _S. berbera_), showed by direct experiments that infection by means of the bites of _Pediculus vestimenti_ and _P. capitis_ was untenable. As many as 4,707 infected lice were fed on one man, and 6,515 on another occasion were allowed to bite a man after they had fed on a monkey heavily infected with spirochætes, yet no infection of the man followed. Examination of the lice showed that the spirochætes left the gut soon after they were ingested, and passed into the body cavity, which swarmed with spirochætes. The contents of the alimentary tract and the fæces of the lice alike were uninfective. The spirochætes did not reappear in the gut till eight days after an infective feed, but some persisted as late as the nineteenth day when kept at 28° C.

[156] _C.R. Acad. Sci._, cliv, p. 1636; clv, p. 481.

It was noted that the irritation due to the lice caused scratching, and that thereby lice became crushed on to the skin. An emulsion was made of two infected lice and rubbed on to the slightly excoriated skin of one of the above workers. Infection followed five days later. A drop of emulsion placed on the conjunctiva of the human eye produced spirochætosis after an incubation of seven days. The body contents of such lice, then, produce infection when they reach the blood by any excoriated or penetrable surface. The stages leading up to infection in nature briefly are: The irritation due to the louse bites causes scratching, and the lice are crushed on to the skin. The slight abrasion is quite sufficient to permit the entry of the parasite. The louse bite alone is harmless. Infection by way of the eye is quite probable in Africa, remembering the constant trouble due to sand, dust, insects, etc., resulting in frequent touching of the eyes.

The spirochætes occur in the body fluid of the lice and can pass in it to the adjacent organs. Thus they probably find their way into the genital organs, and into the eggs of the lice. Eggs laid twenty to thirty days after the parent became infected have retained the infection, and the larvæ issuing from such eggs must have contained some form of spirochætes, for an emulsion of either the eggs or the larvæ produced spirochætosis when inoculated into monkeys. Further details regarding the spirochætosis in the eggs of the lice and in the larvæ are needed. Hereditary infection, however, has been demonstrated, but is not very common. Sergent and Foley (1914) state that the spirochæte possesses a very small and virulent form which it assumes during apyrexial periods in man and during a period following an infecting meal in the louse. Nicolle and Blanc (1914) find that the organisms are infective in the louse just before they reappear as spirochætes. Nicolle and Blaizot found that female lice were more susceptible to spirochætes than males, four times as many females as males being infected.

Tictin (1897) found _S. recurrentis_ in bugs recently fed on
patients, and infected a monkey with the fluids of crushed bugs.
Karlinski (1902) found the spirochætes in bed-bugs in infected
houses. There is some other evidence to show that bugs may transmit
the spirochæte in Nature. Further researches are needed regarding the
relationship of bed-bugs and human spirochætosis.

Multiplication of _S. recurrentis_ is by longitudinal and transverse division (including so-called “incurvation”), and the organism forms small, ovoid bodies (“coccoid” bodies) in the same way as _S. duttoni_.

_S. recurrentis_ is the cause of European relapsing fever, and a number of possible varieties of it are associated with relapsing fevers in other parts of the world. Such spirochætes only differ by biological reactions, such as acquired immunity tests. They include:--

_S. rossii_, the agent of East African relapsing fever; _S. novyi_, the agent of North American relapsing fever; _S. carteri_, the agent of Indian relapsing fever; _S. berbera_, the agent of North African and Egyptian relapsing fever.

OTHER HUMAN SPIROCHÆTES are:--

_S. schaudinni._ This organism, according to Prowazek, is the agent of ulcus tropicum. It varies in length from 10 µ to 20 µ.

_S. aboriginalis_ has been found in cases of granuloma inguinale in British New Guinea and Western Australia. It also occurs in dogs, and may not be truly parasitic.

_S. vincenti._ This spirochæte is 12 µ to 25 µ in length, tapers at both ends and has few coils. It has been associated with angina vincenti. It often occurs in company with fusiform bacilli.

_S. bronchialis_, found by Castellani in 1907 in cases of bronchitis in Ceylon. The parasites are delicate, but show morphological variation. This organism is important and has since been found in the West Indies, India, Philippine Islands and various parts of Africa, such as the Anglo-Egyptian Sudan, Uganda and West Africa. It has recently been the subject of research by Chalmers and O’Farrell, Taylor, and Fantham.

_S. phagedenis_ was found by Noguchi in a ten days old ulcerated swelling of the labium. The organism shows much variation in size, being 4 µ to 30 µ in length.

_S. refringens_ (Schaudinn, 1905) occurs in association with _Treponema pallidum_ in syphilitic lesions, but is non-pathogenic. It is 20 µ to 35 µ long and 0·5 µ to 0·75 µ broad, being larger than _T. pallidum_ and more easily stained.

Various spirochætes have also been notified in vomits, chiefly in Australia; others from the human intestinal tract, _e.g._, _S. eurygyrata_; _S. stenogyrata_ (Werner); _S. hachaizæ_ (Kowalski), in cholera motions; _S. buccalis_ (Cohn, 1875) and _S. dentium_ occurring in the human mouth and in carious teeth (_S. dentium_, Koch, 1877, being the smaller); _S. acuminata_ and _S. obtusa_ found by Castellani in open sores in cases of yaws.

Animal spirochætes of economic importance include:--

_S. anserina_, highly pathogenic to geese.

_S. gallinarum_ (= _S. marchouxi_) in fowls. (See p. 119.)

_S. theileri_ in cattle and _S. ovina_ in sheep also occur in Africa; their pathogenicity is not clear.

_S. laverani_ (= _S. muris_), occurring in the blood of and pathogenic to mice, is probably the smallest spirochæte from the blood, being only 3 µ to 6 µ long.

Numerous spirochætes have been recorded from the guts of various mammals, birds, fishes, amphibia and insects.

CULTIVATION OF SPIROCHÆTES.--Cultures of spirochætes have been made with little success or with great difficulty until comparatively recently, when Noguchi (1912) devised a means whereby he has cultivated most of the pathogenic spirochætes as well as some Treponemata.

Noguchi has now cultivated _S. duttoni_, _S. recurrentis_, _S. rossii_, _S. novyi_ and _S. gallinarum_ from the blood; _S. phagedenis_[157] from human phagedænic lesions; _S. refringens_[158] and spirochætes from the teeth.

[157] _Journ. Exptl. Med._, xvi, p. 261.

[158] _Journ. Exptl. Med._, xv, p. 466.

His method is as follows:--

A piece of fresh, sterile tissue, usually rabbit kidney, is placed in a sterile test-tube. A few drops of citrated blood from the heart of an infected animal, _e.g._, rat or mouse, is added, and about 15 c.c. of sterile ascitic or hydrocœle fluid is poured quickly into the tube. Some of the tubes are covered with a layer of sterile paraffin oil, others are left uncovered. The tubes are incubated at 37° C. The best results are obtained if the blood is taken from an animal forty-eight to seventy-two hours after it has been inoculated, that is, before the spirochætes reach their maximum multiplicative period in the blood. The presence of some oxygen seems indispensable for these blood spirochætes, and they fail to develop _in vacuo_ or in an atmosphere of hydrogen.

For subcultures, 0·5 c.c. of a culture is added to the medium instead of citrated blood, and it is useful to add a little fresh, normal blood, either human or from an animal, such as a rat.

Noguchi found that the events in cultures were:--

_S. duttoni_,[159] maximum multiplication on the eighth to ninth day; disintegration beginning on the tenth day, spirochætes disappeared after about the fifteenth day. No diminution of virulence was found at the ninth day.

[159] _Journ. Exptl. Med._, xvi, p. 202.

_S. rossii_ (= _S. kochi_).[160] Maximum development on the ninth day, after which the virulence diminishes. The incubation period is also prolonged.

[160] _Ibid._, p. 205.

_S. recurrentis_[161] (= _S. obermeieri_). Maximum growth on the seventh day.

[161] _Ibid._, p. 205.

_S. novyi._[162]--Maximum development on the seventh day. It is more difficult to grow than the preceding forms.

[162] _Ibid._, p. 208.

All the above spirochætes showed undoubted longitudinal division and transverse division was observed in part.

_S. gallinarum_[163] can be cultivated as above, but transverse division was usual here. Maximum growth occurred in the culture about the fifth day.

[163] _Ibid._, p. 620.

TREPONEMATA.

The genus _Treponema_ (Schaudinn, 1905), includes minute, thread-like organisms, with spirally coiled bodies, the spirals being preformed or fixed. No membrane or crista is present, according to Schaudinn, though a slight one is said by Blanchard to be present in the organism of yaws. The ends of the organisms are tapering and pointed. Multiplication is by longitudinal and transverse division. The most important members of the genus are _T. pallidum_, the agent of syphilis, and _T. pertenue_, which is responsible for frambœsia or yaws.

*Treponema pallidum*, Schaudinn, 1905.

Syn.: _Spirochæta pallida_.

_Treponema pallidum_ was first described by Schaudinn and Hoffmann in 1905 under the name of _Spirochæta pallida_. It has also been described under the names of _Spironema pallida_, _Microspironema pallida_ and _Trypanosoma luis_. Siegel in 1905 described an organism which he called _Cytorhyctes luis_ and considered to be the agent of syphilis. Schaudinn reinvestigated Siegel’s work and found _T. pallidum_, which he considered to be the causal agent of the disease, and pronounced against _Cytorhyctes luis_. It is probable now that both workers were correct, for Balfour (1911) has seen the emission of minute granules or “coccoid” bodies from _T. pallidum_ and these granules probably correspond to the _C. luis_ of Siegel. Recently E. H. Ross, having observed a spirochæte stage in the development of Kurloff bodies, thinks that _T. pallidum_ is a stage in the life-history of a Lymphocytozoon. MacDonagh has also described a complicated and somewhat similar cycle, but these observations require further study and confirmation.

_T. pallidum_ varies from 4 µ to 10 µ in length, its average length being 7 µ, while its width is usually about 0·25 µ. Longer individuals of 16 µ to 20 µ have been recorded. The body has from eight to ten spiral turns and forms a tapering process at each end (fig. 56). The organism is most difficult to stain, and its internal structure is little known. It is possibly like that of _Spirochæta duttoni_ or _S. balbianii_, as the “granule shedding” observed by Balfour is strongly suggestive of the formation of resistant bodies by those spirochætes. Hoffmann (1912) has seen the formation of spores in _T. pallidum_.

The Treponemata occur in the primary and secondary sores, but are difficult to find in the tertiary eruptions of syphilis. Noguchi and Moore (1913) and Mott[164] (1913) have demonstrated _T. pallidum_ in the brain in cases of general paralysis of the insane. Marie and Levaditi (1914), however, consider that the treponeme found in the brain in such cases is different from _T. pallidum_.

[164] _Brit. Med. Journ._, Nov. 15, 1913. p. 1, 271.

CULTIVATION _of T. pallidum_.--This has been accomplished successfully by Noguchi,[165] using a modification of his method for spirochæte cultivation, for _T. pallidum_ is much more difficult to grow than spirochætes, being a strict anaerobe.

[165] _Journ. Exptl. Med._, xv, p. 90; xvi, p. 211.

The apparatus consists of two glass tubes, the upper being connected to the lower by a narrower tube passing through a rubber cork (fig. 57). Both tubes are carefully sterilized.

A piece of fresh, sterile rabbit’s kidney is placed in the lower tube, which is filled with ascitic fluid, or ascitic fluid and bouillon mixture. The tube is inoculated with syphilitic material and corked by inserting the upper tube. In the bottom of the upper tube a piece of sterile rabbit’s kidney is placed and syphilitic material poured over it. A mixture of one part ascitic fluid and two parts of slightly alkaline agar is then poured over the tissue and allowed to solidify. When solid, a layer of sterile paraffin oil is poured on top of it, and the top plugged with cotton wool (fig. 57). The whole is then incubated at 37° C. for two or three weeks. The tissue removes traces of oxygen from the lower levels of the medium and also probably provides a special form of nourishment. At first _T. pallidum_ grows in the solid medium, and then when the cultural conditions in the lower fluid portion become favourable, the organisms migrate thither and multiply abundantly. At first the culture is impure, but after several transferences a pure culture is obtained readily.

The syphilitic material for culture is prepared by cutting off pieces of tissue from the lesions, washing in sterile salt solution containing 1 per cent. sodium citrate, and then emulsifying the tissue in a mortar with sodium citrate.

Good cultures show rapid multiplication, which is invariably by longitudinal division.

In his various cultivation experiments Noguchi[166] found morphological and pathogenic variations in _T. pallidum_. Three forms of the organism were found, namely, thicker, average and thinner types. The lesions caused in the testicle of the rabbit differ according to the variety inoculated, but more work is necessary on the subject.

[166] _Journ. Exptl. Med._, xv, p. 201.

Noguchi[167] has cultivated a separate organism, _T. calligyrum_, from the surface of human genital or anal lesions, either syphilitic or non-syphilitic. It is apparently non-pathogenic, and is 6 µ to 14 µ long.

[167] _Journ. Exptl. Med._, xvii, p. 89.

Hata (1913)[168] has modified the Noguchi technique for the cultivation of spirochætes and treponemes, with a view to simplification and convenience. Hata substitutes normal horse serum for ascitic fluid and the “buffy coat” of the clot of horse blood in place of the small pieces of rabbit’s kidney. It is unnecessary to place sterile paraffin on the surface of the medium.

[168] _Centralbl. f. Bakt._, Orig., lxxii, p. 107.

The horse serum is mixed with twice its volume of physiological saline solution. The mixture is placed in tubes which are heated on a water-bath at 58° C., the temperature being raised gradually until it reaches 70° or 71° C. in three hours. The tubes are then heated at 71° C. for half an hour. After cooling, the contents will consist of an opaque semi-coagulated mass. This semi-coagulated serum and saline mixture may be substituted for Noguchi’s ascitic fluid.

The buff coagulum is cut into small pieces, about 1 c.c. in volume. They must be forced with a sterile glass rod to the bottom of the semi-coagulated serum and saline mixture. The medium is inoculated with a small quantity of infected blood and kept at 37° C. In the case of _S. recurrentis_, growth of spirochætes is observed on the second day, reaching a maximum in five to seven days. The growth of the organisms proceeds rather more slowly, they live for a longer period and maintain their virulence better than in Noguchi’s medium.

*Treponema pertenue*, Castellani, 1905.

Syn.: _Spirochæta pertenuis_; _S. pallidula_, Castellani, 1905.

Castellani discovered the organism in 1905, in scrapings of yaws pustules. He first described it under the name of _Spirochæta pertenuis_.

_Treponema pertenue_ (fig. 58), though delicate and slender, shows great morphological variation both in length and thickness. It may be short, _e.g._, 7 µ, but can attain 18 µ to 20 µ in length and may be even larger. In cultures made by Noguchi, thick, medium and thin forms were found, each giving rise to a different type of frambœsial lesion when inoculated into the testicles of rabbits, thus suggesting the possibility of the occurrence of varieties of _T. pertenue_.

The organism is difficult to stain, but occasionally deeper staining granules are found along its body. They may represent a diffuse nucleus. Granule formation similar to that of _T. pallidum_ has been observed by Ranken, using dark-ground illumination.

Many experiments have been made with a view to establishing the identity of the organism of yaws and also of differentiating between the causative agents of yaws and syphilis. Both monkeys and the human subject have been experimentally inoculated with yaws material and have developed the disease.

In an early experiment, negroes were inoculated with the secretion from lesions of yaws. All of them developed the disease, nodules appearing, chiefly at the seat of inoculation, in from twelve to twenty days, followed by the usual eruption. Similar results were obtained with thirty-two Chinese prisoners, who were inoculated with yaws, twenty-eight becoming infected.

A naturally infected yaws patient when inoculated with syphilis, contracted that infection, thus showing that yaws does not confer immunity to syphilis. This has also been observed naturally, when yaws patients have contracted syphilis.

Experiments with monkeys have been successfully performed. The incubation period varies from sixteen to ninety-two days. Lesions appear first at the seat of inoculation, and in some monkeys the eruption is localized to this spot, though the infection is general, _T. pertenue_ occurring in the spleen, lymphatics, etc. Monkeys inoculated with splenic blood of a yaws patient, and also sometimes with blood from the general circulation, have become infected.

Castellani and others have shown that monkeys successfully inoculated with syphilis do not become immune to yaws, and vice-versâ.

Craig and Ashburn, using the monkey _Cynomolgus philippinensis_, found these animals susceptible to yaws but not to syphilis.

The ulcerated lesions of frambœsia are rapidly invaded by numerous bacteria as well as by different spirochætes, of which Castellani has described three distinct species. One is identical with _Spirochæta refringens_, Schaudinn, the other two are thin and delicate. One, _S. obtusa_, has blunt ends; the other _S. acuminata_, has pointed ends. _T. pertenue_ is also present.

The reasons for considering _T. pertenue_ to be the specific cause of frambœsia are:--

(1) _T. pertenue_ is the only organism present in non-ulcerated papules, in the spleen and in the lymphatics of yaws patients, or of monkeys artificially infected with the disease. By no method has any other organism been obtained.

(2) Extract of frambœsia material, free from all organisms other than _T. pertenue_, reproduces the disease if inoculated.

(3) Extract of frambœsia material deprived by filtration of _T. pertenue_ is no longer infective on inoculation.

The method of infection is contaminative, by direct contact. Women in Ceylon are frequently infected by their children. Any slight skin abrasion is sufficient to admit the parasite. In some cases, insects may carry the disease from person to person, and even in hospitals, when dressings are removed, it has been noticed that flies greedily suck the secretion from the ulcers. _T. pertenue_ has been recovered from flies that have fed on yaws, and monkeys have contracted the disease when flies were placed and retained on them for a short time, after the insects had fed on yaws material.

CULTIVATION.--_T. pertenue_ has been cultivated by Noguchi, who finds three types of parasites in his cultures, as before mentioned. Its multiplication is by longitudinal division.

Noguchi[169] (1912), has cultivated species of Treponema from the human mouth, e.g., _T. macrodentium_, _T. microdentium_ and _T. mucosum_, the latter from pyorrhea alveolaris. These parasites in the past may have been confused under the name _Spirochæta dentium_.

[169] _Journ. Exptl. Med._, xv, p. 81; xvi, p. 194.

Class III. *SPOROZOA*, Leuckart, 1879.

The third group of the Protozoa consists entirely of parasitic organisms forming the class known as the Sporozoa or spore-producing animals. The members of this class are characterized by possessing very great powers of multiplication, coupled with a capacity for producing forms that serve for the transference of the organisms to other hosts. These reproductive bodies, whether for increase of numbers within one host or for transmission to another host, are called spores. But, strictly, the term spore should be used only in the latter connection, when a protective or resistant coat known as a sporocyst envelops the body of the spore.

The Sporozoa are widely distributed, occurring in various tissues and organs of Annelids, Molluscs, Arthropods, and Vertebrates. Their food, which is fluid, is absorbed osmotically. The life-cycle of a Sporozoön may be completed within one host or may be distributed between two different hosts.

The Sporozoa were divided by Schaudinn into two groups or sub-classes, called (1) the *Telosporidia*, and (2) the *Neosporidia*.

The Telosporidia are Sporozoa in which the reproductive phase of the parasites is distinct from the growing or trophic phase, and follows after it. The Neosporidia include Sporozoa in which growth and spore-formation go on simultaneously. This classification is not final, for certain exceptions and difficulties are already known with regard to it. It is possible that the class Sporozoa is not a natural entity, but should be replaced by two classes of equal rank, corresponding in most respects with the Telosporidia and Neosporidia.

The *Telosporidia* comprise the *Gregarinida*, the *Coccidiidea*, and the *Hæmosporidia*. Doflein combines the two latter orders into one known as the *Coccidiomorpha*.

The *Neosporidia* comprise the *Myxosporidia*, the *Microsporidia*, the *Actinomyxidia*, the *Sarcosporidia*, and the *Haplosporidia*. Doflein combines the first three orders into one, the *Cnidosporidia*.

Sub-Class. TELOSPORIDIA, Schaudinn.

Sporozoa in which the reproductive phases follow completion of growth.

Order. *Gregarinida*, Aimé Schneider emend. Doflein.

Knowledge of the Gregarinida probably goes back as far as the year
1684, when Redi observed gregarines in the crab, _Cancer pagurus_.
Von Cavolini (1787) found them in _Cancer depressus_. The name
_Gregarina_ was created by L. Dufour (1828), who observed masses
of these organisms in the gut of insects of different orders.
Hammerschmidt (1838) and von Siebold found rich infestations in
insects, while Dujardin (1835) and Henle described various genera
from segmented worms. Henle (1835) also observed cysts containing
“navicellæ” in the sperm-sacs of segmented worms, and attention was
drawn to his researches by the discovery by von Siebold (1839) of
“pseudonavicellæ” in the gut of _Sciara nitidicollis_. Up to this
time many workers considered the gregarines to be worms, but Kölliker
(1845) investigated many of them and maintained their unicellular
nature, while Stein’s work (1848) showed the interrelation of the
pseudonavicellæ and the gregarines. The discovery of amœboid germs
in the pseudonavicellæ by Lieberkühn (1855) and the demonstration of
myonemes further aided in the elucidation of their true systematic
position. The entire process of conjugation, of which Dufour had seen
one phase, was followed by Giard under the microscope.

From 1873 onwards Aimé Schneider made important additions to the
knowledge of the morphology, life-history, and systematic position
of numerous gregarines. Bütschli (1881) and L. Léger (1892) also
contributed much work on the subject. The discoveries of Schaudinn
with regard to the life-cycle of Coccidia gave a fresh stimulus to
the study of the Gregarines, whereby the life-cycles of numerous
forms and the phases thereof have been elucidated.

Asexual multiplication is not common among the Gregarines, but is
known to occur in the sub-order Schizogregarinea, formerly known as
the Amœbosporidia.

Although the Gregarinida are not known to be parasitic in man or
other vertebrates, they are of great interest, inasmuch as they are
among the earliest known Sporozoa, and therefore will be briefly
described here.

The Gregarines are usually elongate, somewhat flattened organisms (figs. 59, 60), whose bodies are enclosed in an elastic and often thick cuticle. The enclosed living substance shows a separation into ectoplasm and endoplasm, as is common among Protozoa. The cuticle is sometimes regarded as the outer portion or epicyte of the ectoplasm. A single, vesicular, spherical, or elliptical, large nucleus, with its chromatin concentrated to form a spherical karyosome, is present. The body of some gregarines may be divided by ingrowing ectoplasmic partitions or septa, and are then said to be “septate” or “polycystid” (fig. 61). Other gregarines remain simple and non-septate, and are termed “monocystid” (fig. 59). The monocystid gregarines occur especially in the body cavity of Chætopoda and Insecta, more rarely in Echinodermata, in the parenchyma of Platyhelminthes, also in the gut of Tunicata and Insecta (fig. 60) and in the seminal vesicles of Annelida. In the polycystid gregarines a single septum only is present as a rule, and thus the body presents two portions: (1) an anterior portion termed the protomerite; (2) a posterior, larger portion, known as the deutomerite, which generally contains the nucleus. The protomerite is often modified anteriorly to form an organ of attachment, termed the epimerite (fig. 61), which is developed from the pointed rostrum of the sporozoite or primary infecting young gregarine. The structure of the epimerite may be complicated, being provided with hooks, spines, knobs, and other appendages. An extension of the polycystid condition is seen in _Tæniocystis mira_ Léger (from the dipteran larva, _Ceratopogon solstitialis_), whose body shows a number of partitions, giving the organism a superficial resemblance to a tapeworm.

The ectoplasm of a gregarine exhibits three layers: (1) An epicyte (cuticle) externally of which the epimerite is composed; (2) a sarcocyte which forms the septa if present; (3) the deeper myocyte layer containing contractile elements in the form of fibrils or threads termed myonemes (fig. 62).

The endoplasm is fluid and granular, containing many enclosures, which are of the nature of reserve food materials. They consist of fat droplets or of paraglycogen, and give the organisms an opaque appearance. _Lithocystis_ contains crystals of calcium oxalate in its endoplasm.

Many gregarines are capable of active movements, though they do not possess obvious locomotor organs. The movement is of a smooth, gliding character and two suggestions have been put forward to explain it. According to Schewiakoff, a gelatinous substance is secreted between the layers of the ectoplasm. This is extruded posteriorly and thus the animal is pushed forward. On the other hand, Crawley considers that the movements are produced by contractions of the myonemes. These two explanations are probably correct as far as each goes, and are to be regarded as supplementary to one another.

Occasionally, temporary associations of gregarines are formed by a number of individuals adhering to one another end to end. Such temporary associations are examples of syzygy. Such syzygies must not be confused with true associations which form an essential part of the life-cycle.

The life-cycle of a relatively simple gregarine, such as _Monocystis agilis_ (fig. 59), parasitic in earthworms, may now be considered. The gregarines, being members of the Sporozoa, produce spores at one phase of the life-cycle. Each gregarine spore (fig. 63) develops within itself a number of minute, sickle-shaped or vermicular bodies, known as sporozoites or primary infecting germs. Eight sporozoites are often formed within each spore. When absorbed by a new host, the spore softens and the sporozoites issue from it. They are capable of active movement and may or may not enter a cell, such as one of those of the digestive tract, or, as in _Monocystis_, a cell lining the vesicula seminalis which becomes a sperm-cell aggregate (sperm morula). When the sporozoite has reached the place of its choice in the host it ceases active movements and proceeds to feed passively on the fluid substances around it, whether they be those of tissues or body fluids. This passive, growing and feeding form is known as the trophozoite. After a trophic existence of longer or shorter duration, the trophozoite ceases to feed and prepares for reproduction. Two trophozoites associate together, each of them first becoming somewhat rounded. The two trophozoites, now known as sporonts or gametocytes, become invested in a single common envelope or cyst (fig. 64, _a_). The nucleus of each gametocyte then divides by a series of binary fissions (fig. 64, _b_), and the daughter nuclei thus produced arrange themselves at the periphery of the parent cells (fig. 64, _c_). Cytoplasm collects around each of these nuclei, and thus a number of gametes are formed within each gametocyte. The gametes for a time exhibit active movements, and ultimately ripe gametes of different parentage fuse in pairs, that is, conjugation occurs (fig. 64, _d_). In this way zygotes are produced, the nucleus of each zygote being formed by the fusion of two gamete nuclei.

The zygote grows slightly and becomes oval or elongate, and at this period is often called the sporoblast. It then secretes an external membrane, the sporocyst. Nuclear division occurs inside the sporocyst by a series of three binary fissions (fig. 64, _e_), so that each sporocyst, now usually referred to as a spore, contains eight nuclei. The cytoplasm collects around each nucleus and eight vermicular sporozoites are produced within each spore (fig. 64, _f_), thus completing the life-cycle.

It will be noticed that in the above life-cycle no asexual multiplication occurs. These organisms, such as _Monocystis_, are known as the Eugregarines, and include the majority of the gregarines. The remainder, which have introduced schizogony into their life-cycle, are known as the Schizogregarines.

There are variations in the morphology and life-cycle of gregarines besides those that have been mentioned. It is not within the scope of this book to discuss them in detail, but the following may be noted:--

Morphological differentiation of gametes may occur as in _Stylorhynchus oblongatus_ (fig. 65), which differentiation is probably of a sexual nature.

The sporocyst really consists of two layers, an epispore and an endospore. Externally the spores of different gregarines show great variety in shape and markings, and spines, or long processes may be present (fig. 66).

The resistant spores serve for the transmission of the gregarines from host to host. The mode of infection is contaminative, the spores expelled with the dejecta of one host being absorbed with the food of a new host.

The Gregarinida may be classified as follows:--

Sub-order I.--*Eugregarinea*, without schizogony.

Tribe 1.--_Acephalina_.--Without an epimerite and non-septate; often “cœlomic” (body-cavity) parasites. _E.g._: _Monocystis_, with several species parasitic in the seminal vesicles of earthworms. Many other genera parasitic in Echinodermata, Tunicata, Arthropoda, etc.

Tribe 2.--_Cephalina_.--With an epimerite, either temporarily or permanently, in the trophic phase. Usually septate (except _Doliocystidæ_). Many families, genera and species. Common in the digestive tracts of insects. _E.g._: _Gregarina_, with several species, _Gregarina ovata_ in the earwig, _Gregarina blattarum_ in the cockroach, _Stylorhynchus_ in beetles, _Pterocephalus_ in centipedes, etc.

Sub-order II.--*Schizogregarinea*, with schizogony.

Tribe 1.--_Endoschiza_.[170]--With schizogony occurring in the intracellular phase, _e.g._, _Selenidium_ (from Annelida and Gephyrea), _Merogregarina_ (from an Ascidian).

[170] See Fantham (1908), _Parasitology_, i, p. 369.

Tribe 2.--_Ectoschiza_.--In which the schizont is free, and schizogony is extracellular, _e.g._, _Ophryocystis_ (from _Blaps_, a beetle), and _Schizocystis_ (from _Ceratopogon_ larva).

Order. *Coccidiidea*.

Hake (1839) first saw the organisms now termed Coccidia during
his investigations on the so-called coccidial nodules of rabbits.
The opinions as to the nature of these peculiar formations were
very diverse. The discoverer considered them to be a sort of pus
corpuscle; Nasse (1843) took them for epithelial cells of the biliary
passages, others for helminthes, especially the ova of trematodes
(Dujardin, Küchenmeister, Gubler, etc). Remak (1845) was the first to
draw attention to their relation to the Psorospermia (Myxosporidia),
and this investigator found them also in the small intestine and
vermiform appendix of rabbits. Lieberkühn (1854), who examined
not only the coccidia of rabbits, but found similar forms in the
kidneys of frogs, likewise called them definitely psorosperms. To
differentiate Müller’s psorosperms, which are found in fishes, from
those of rabbits, etc., the latter were called egg-shaped psorosperms
(Eimer), until R. Leuckart (1879) named them _Coccidia_ and placed
them in a group of the Sporozoa analogous to that of the Gregarinida,
Myxosporidia, etc. Numerous works confirmed the occurrence of
coccidia, not only in all classes of vertebrate animals, but also in
invertebrates (Mollusca, Myriapoda, Annelida, etc.). A large number
of genera and species have in the course of time been described
which inhabit the epithelium of the intestine and its appendages for
choice, but are also found in other organs (kidneys, spleen, ovaries,
vas deferens, testicles). Some also live in the connective tissue of
various organs, more particularly of the intestine.

The knowledge of the development of the coccidia was of particular
importance in determining their classification. By means of encysted
coccidia from the liver of rabbits, Kauffmann (1847) first confirmed
the fact that the cyst, which was partly or entirely filled with
granular contents, divided into three or four pale bodies (fig. 71)
after a long sojourn in water. Lieberkühn observed the same process
in the host in the case of the coccidia of the kidney of the frog.
Stieda (1865) studied more minutely the changes that occur within
the encysted coccidia of the liver of rabbits after the death of
the host. He discovered that the bodies now known as “spores” were
oval formations pointed at one pole, and surrounded by a delicate
membrane, which exhibited a certain thickness at the pointed
extremity and enclosed a slightly bent rodlet, expanding at either
end into a strongly light-refracting globule; a finely granular
globule was present in the middle of the spore. Waldenburg (1862) saw
the same phenomenon in coccidia from the epithelium of the villi and
Lieberkühn’s glands of the intestine of the rabbit; but the process
in this case took place in a much shorter time.

According to the discovery of Kloss (1855), the spores of the
coccidia of the urinary organ of the garden snail were formed in far
greater numbers: the round spores also harboured several (five to
six) rodlets, which after the bursting of the spore-envelope became
free. Eimer’s researches (1870) afforded information regarding a
Coccidium from the intestine of the mouse, which was transformed
_in toto_ into a “spore,” containing small sickle-shaped bodies.
The fact was, moreover, established that the little bodies left the
delicate envelope when in the intestine, made movements of flexion
and extension, and were finally transformed into amœboid organisms,
which apparently penetrated the epithelial cells; at all events,
similar bodies of various sizes were seen in these cells. Taking the
immense number of these parasites into account and the lack of any
other cause, Eimer attributed the sudden death of his mice to the
_Gregarina falciformis_, as the parasite was then called, just in the
same way as a few years previously Reincke ascribed the acute and
fatal intestinal catarrh of rabbits to the invasion of intestinal
coccidia.

All that had become known about coccidia up to 1879 was then
compiled by Leuckart, and completed by his own observations on
the coccidia of the liver of the rabbit. Experimental infections
had already been conducted by Waldenburg (1862) with intestinal
coccidia of rabbits, and by Rivolta (1869–73) with the coccidia of
fowls, which experiments confirmed the importance of the spores,
or bodies enclosed in them, in the transmission of the parasites
to other animals. Accordingly, it was assumed that after the entry
of the spores into the intestine the sporozoites were set free,
actively penetrated into the intestinal cells, where they grew into
coccidia, and finally became encysted. The further development,
_i.e._, the formation of spores, took place outside the host’s body
in these cases; in other cases (Kloss, Eimer) it took place within
the host. Although much regarding the cycle of development was still
hypothetical, the ideas coincided with the observations, and were
therefore universally regarded as established. Further research
confirmed this view in numerous new forms.

L. Pfeiffer’s statements (1891) on the part that certain coccidia or
their sporozoites played, or seemed to play, as causes of disease
gave a renewed impetus to the investigation of the coccidia. The
ingestion of even very numerous spores did not appear to account for
the mass infection so frequently observed, even after Balbiani had
confirmed the fact that there were two, and not one, sporozoites
contained in every spore of the coccidia of rabbits (fig. 72). The
hypothesis was therefore advanced that the sporozoites or young
coccidia were able to divide once again by sporulating. The question
was finally solved quite differently. R. Pfeiffer (1892) first
confirmed the fact that in addition to the well-known method of
sporulation in the coccidia of the rabbit that causes the infection
of fresh hosts (“exogenous sporulation”), an enormous increase may
follow in the already infected host in a manner that Eimer first
observed in the coccidia of the intestine of the mouse (“endogenous
sporulation”). It had hitherto been believed that some of the
species of coccidia increased like the rabbit parasite, then known
as _Coccidium oviforme_, and others like _Eimeria falciformis_, and
this difference had been made the foundation of a classification. R.
Pfeiffer was successful in observing the occurrence of both kinds
of development in the same species, and expressed the opinion that
endogenous sporulation (fig. 73), which takes place within the host,
was the cause of the mass-infection that is mostly accompanied by
serious consequences (fig. 74). L. Pfeiffer sought, especially, to
demonstrate the correctness of this view as regards other species of
coccidia and for this purpose he utilized the experiences already
published. Coccidia were known to exist in a number of different
hosts, and to propagate in some according to the _Coccidium_ type,
in others according to the _Eimeria_ type. It therefore was reasoned
that in this case it was not a question of two species belonging
to different genera living side by side, with a different mode of
development, but of one species, in the life of which both forms of
development occurred alternately.

This interpretation of facts was combated especially by A. Schneider
(1892) and by Labbé, but has, nevertheless, proved true, apart from
the circumstance that Schuberg succeeded in discovering the hitherto
unknown _Coccidium_ form in the intestine of the mouse; and that,
moreover, Léger confirmed the fact that there are no Arthropoda in
which Eimeria are not found together with coccidia. The question
was finally settled by experiments made by Léger with the coccidia
of _Scolopendra cingulata_, by Schaudinn and Siedlecki with those
of _Lithobius forficatus_, and by Simond with the coccidia of the
rabbit. On Simond’s suggestion the sickle-shaped germs corresponding
to the sporozoites, which are formed by endogenous sporulation, are
generally termed merozoites; and in accordance with Schaudinn’s
suggestion, those individuals which form merozoites are termed
schizonts, and those which produce spores are called sporonts. In
contradistinction to sporogony (exogenous sporulation), the term
schizogony (endogenous sporulation) is used.

The more minute examination of these processes at last led to the
discovery of sexual dimorphism, of copulation and of alternation of
generations in the coccidia. Schuberg was the first to consider the
possibility of copulation in coccidia; in addition to the formations
which now are termed merozoites, he observed very diminutive
bodies (“microsporozoites”) in the coccidia of the intestine of
the mouse, which were able eventually to copulate. Labbé confirmed
this observation in some of the species, and Simond expressed
the opinion that bodies termed “chromatozoites” occurred in all
coccidia. Copulation itself was then observed by Schaudinn and
Siedlecki (1897). The copulating bodies were termed gametes. As,
however, they differed considerably one from the other, the males
were called microgametes (_i.e._, the microsporozoites of Labbé and
the chromatozoites of Simond) and the females macrogametes. After
copulation was completed sporogony took place, and in the cycle of
development of one species this regularly alternated with schizogony
(asexual multiplication). Schaudinn in 1900 described in detail the
life-cycle of _Eimeria_ (_Coccidium_) _schubergi_.

The recognition of this unsuspected complicated process was bound to
effect reforms in the classification of the coccidia; and all the
forms that had been regarded as developmental stages (_Eimeria_,
etc.) had to be reconsidered.

_Occurrence._--The Coccidiidea in their mature condition usually live within the epithelial cells of various organs, and by choice inhabit those of the intestine and of its associated organs. They also occur frequently in the excretory organs of mammals, birds, amphibia, molluscs, arthropods, and may also be found in the testes and vas deferens, but the statement that they live in hen’s eggs, as well as in the oviducts of fowls, has not been confirmed.[171] Some species inhabit the nuclei of cells, others live in the connective tissue, but their presence in the latter situation is probably only secondary, that is, they have only reached it from the epithelium of the affected organs.

[171] Notwithstanding the progress made during the last decades, the ova of helminthes and more particularly of trematodes, have been mistaken for Coccidia. Thus Poschinger (_Zool. Anz._, 1819, ix, p. 471) and Gebhard (_Virchow’s Arch._, 1897, No. 147, p. 536) mistook the ova of _Distoma turgidum_, Brds., for Coccidia. Podwyssotzki (_Centralbl. f. allg. Path._, 1890, i, p. 135) made a similar error with the ova (and vitelline sacs) of a species of _Prosthogonimus_ (_Distoma ovatum_ of the authors); von Willach (_Arch. f. wiss. u. prakt. Thierheilk._, 1892, xviii, p. 242) mistook the ova of a nematode for Coccidia.

The size of the Coccidiidea, corresponding as a rule to the capacity of their habitat, is usually small, but there are said to be species that attain a diameter of 1 mm. Their form[172] is globular, oval, or elliptical. External appendages are lacking, at least during the trophic or vegetative period of their life, which is spent in epithelial cells, within which they increase in size. Frequently one only is present in each cell, but more can occur. The body substance is composed of a more or less finely granular or distinctly alveolar protoplasm which exhibits no differentiation into ecto- and endoplasm. All species possess a nucleus that enlarges with their growth; sometimes it only shows through the cytoplasm as a lighter spot, or may even be quite concealed. It is vesicular, and besides containing very delicate threads of chromatin in the clear nucleoplasm, it contains generally only one large karyosome.

[172] The life-cycle given here is based on that of _Eimeria_ (_Coccidium_) _schubergi_, after Schaudinn (1900). See “Untersuchungen über den Generationswechsel bei Coccidien,” _Zool. Jahrb., Abt. f. Anat._, xiii, pp. 197–292, 4 plates.

The infected epithelial cells degenerate sooner or later as the parasite feeds on them (fig. 67, II-IV). After their form has been changed by the action of the growing parasite, they finally perish. The cell membrane then alone surrounds the coccidia, which, at least in the species sufficiently known, begin to propagate by an asexual process (schizogony), the parasites themselves becoming schizonts, as the initial stage is usually called. They differ from later stages (sporonts or gametocytes), which resemble them in form, by the absence of granulations in the cytoplasm, as well as by the vesicular nucleus. The form is not always the same, for in some cases, at least, many schizonts assume a globular form.

Schizogony (fig. 67, V-VII) commences with a division of the nucleus, which takes place in different ways in the various species. This finally leads to the formation of numerous daughter nuclei which become smaller and smaller, and which collect beneath the surface of the schizonts. In some species the daughter nuclei collect only in one half of the schizont. A part of the protoplasm of the periphery now divides around each daughter nucleus, the remaining part (residual body) being left in the centre or on one side. The segments of the divided cytoplasm, each containing a nucleus, assume a fusiform shape and become merozoites, which very soon become free (fig. 67, VIII) and leave the residual body. They are distinguishable from the very similar sporozoites (fig. 67, I), as the merozoites possess a karyosome.

The merozoites move in a manner similar to that of the sporozoites.
The movements consist either of slow incurvations with subsequent
straightenings, or annular contractions along the entire extent
of the body. In addition, there are gliding movements similar to
those of many gregarines, and brought about in a like manner by the
secretion at the posterior extremity of a gelatinous substance that
hardens rapidly.

The merozoites do not gain the open in the usual way, but are destined to infect still further the same host by actively penetrating into other epithelial cells of the affected organ. Here they continue their growth and may again and again undergo schizogony. In the Infusoria the repeated segmentations finally cease and are renewed only after a conjugation. This is likewise the case with the Coccidia, with the difference that in the latter the two conjugating individuals (gametes) are differently constituted one from the other, whereas in the Infusoria they are almost always similar.

When the schizogony ceases, the merozoites, that had penetrated the epithelial cells and become trophozoites there, consist of two kinds of differently constituted individuals. One kind possesses a clear cytoplasm (fig. 67, XII), the other an opaque, richly granular cytoplasm (fig. 67, XI), while both possess a vesicular nucleus with a karyosome. In order to continue their development, the more granular individuals must be fertilized, and are therefore termed either female gametes or, on account of their size, macrogametes. The male individuals (microgametes) necessary to conjugation, are formed in greater numbers from the less dense microgametocytes or male mother-cells (fig. 67, XIId). They are slender bodies consisting chiefly of nuclear substance, and in most species bear two flagella of unequal length directed backwards, the place of insertion of which varies according to the species (fig. 67, XIIe).

While the development of the microgametes is rapidly advancing a change occurs in the nucleus of the female parent forms or macrogametocytes. Parts of the karyosome are extruded (fig. 67, XIc), and the nucleus loses at the same time its vesicular form. One macrogamete results, after nuclear maturation, from one macrogametocyte. By this time the macrogametes are capable of conjugation, and the process takes place within the host, generally, however, outside the affected and degenerated host cells. The microgametes that have now become free from the very large residual body, crowd around the mature macrogametes, which often send out a small prominence (“cone of reception” or fertilization protuberance) for their reception (fig. 67, XIII). As soon as a microgamete comes in contact with this and penetrates into the cytoplasm of the macrogamete, the latter surrounds itself with a membrane which prevents the intrusion of other microgametes. The nucleus of the microgamete that has gained entry unites with the nucleus of the macrogamete, which latter is afterwards capable of forming the well-known spores. The parasite is now called an encysted zygote or oöcyst. The oöcysts of some other members of the Coccidiidea, _e.g._, _Eimeria avium_, can form their walls prior to fertilization. In such cases, a weak spot is left at one place in the cyst wall, forming a micropyle, that permits of the entry of the male, immediately after which the micropyle is closed.

The reduced nucleus of the macrogamete elongates on the entry of the
microgamete, and becomes a fertilization spindle to which the male
pronucleus (from the microgamete) becomes attached (fig. 67, XIV and
XV). Thereupon the spindle divides into two daughter nuclei (fig. 67,
XVI) which assume a round shape. The protoplasm at this stage may
at once divide, or another segmentation of the daughter nuclei may
first occur. In the former case the two halves divide again, so
that finally four nucleated segments, the sporoblasts, are formed,
whereas in the latter case the four sporoblasts appear simultaneously
(fig. 67, XVII). In both cases a residual body of varying size is
separated from the protoplasm of the oöcyst. As a rule the oöcysts
have already been discharged from the body of the host, and in the
manner described above, form the sporoblasts after a longer or
shorter period of incubation.