336 THE PROTOZOA 



the body to the exterior. Usually it passes out per anum with the 

 faeces, but when the spores are formed in some internal organ of 

 the body, as in the Monocystis of the earthworm, it may be necessary 

 for the host to be eaten by some other animal, which then scatters 

 the spores broadcast in its faeces. In all cases, so far as is known, 

 the new host is infected by the casual or contaminative method, 

 and in its digestive tract the spores germinate and liberate the 

 sporozoites. In the case of Cystobia minchinii, parasite of Cucu- 

 maria, it is extremely probable that the host acquires the infection 

 by taking up the spores per anum into its respiratory trees, where 

 the spores germinate (Woodcock). 



The schizogony characteristic of the schizogregarines takes 

 place during either the second or third of the phases described in 

 the foregoing paragraphs, in trophozoites derived from the^ sporo- 

 zoites by growth, and it takes various forms which cannot be 

 described in general terms ; a few examples must suffice. 



1. Sdenidium cauUeryi (Fig. 148) : The sporozoite penetrates into a cell 

 of the intestinal epithelium, and grows to a large size, remaining uninucleate. 

 When full-grown, the intracellular parasite gives rise by a process of multiple 

 fission to a great number of motile merozoites which penetrate into epithelial 

 cells, grow, and finally become free sporonts. The schizogony of Merogre- 

 garina amaroucii (Porter) is of a similar type, but fewer merozoites are produced 

 by the schizont. 



2. In Schizocystis gregarinoides (Fig. 149) the sporozoite attaches itself by 

 its rostrum to an epithelial ceil, and as it grows in size its nuclei multiply ; 

 it finally becomes a multinucleate schizont of very large size, which may be 

 either vermiform, and is then attached by an anterior sucker-like organ to 

 the epithelium, or massive in form, and quite free. When full-grown, its 

 body divides up into as many small merozoites as there are nuclei. The 

 merozoites may probably repeat this development and multiply by schizogony 

 again ; or a merozoite may grow, without multiplication of its nucleus, into a 

 sporont, which proceeds to sporogony of a typical kind. In Schizocystis 

 sipunculi (Dogiel, 603) the schizont has a principal nucleus near its anterior 

 end, and forms a number of secondary nuclei near the hinder end of the body, 

 apparently from chromidia given off from the principal nucleus, which loses 

 its chromatin. Round the secondary nuclei protoplasm aggregates, and 

 finally about 150 to 200 merozoites are formed, lodged in a cavity in the cyto- 

 plasm of the schizont. The principal nucleus and the maternal body of the 

 schizont now degenerate, and the merozoites are set free. 



3. In Porospora gigantea of the lobster, the largest gregarine known, the 

 full-grown individuals round themselves off, become encysted singly, and divide 

 up to form an immense number of so-called " gymnospores " (Fig. 150), each of 

 which consists of a cluster of merozoites grouped round a central mass of 

 residual protoplasm. The subsequent development and the aporogony are 

 unknown ; the schizogony was formerly mistaken for the sporogony (Leger and 

 Duboscq, 621). 



In the species Porospora legeri, recently described by Beauchamp (592) 

 from the crab Eriphia spinifrons, a similar process of schizogony is recorded ; 

 but in this case an associated couple or syzygy of two trophozoites becomes 

 encysted together, to undergo a similar process of non sexual multiplication. 

 The association is one of two septate trophozoites closely attached, with loss 

 of the protomerite in the posterior individual, as in Didymophyes ; the subse- 

 quent development and sporogony are unknown. Leger and Duboscq (622) 



