344 THE PROTOZOA 



in the sequel, together with a brief summary of the chief variations 

 which each phase may exhibit in other coccidia. 



1. The spoxozoites, liberated in the digestive tract, are small 

 gregarinulae which move by gliding movements, and penetrate 

 into epithelial cells by means of their pointed anterior end 

 (Fig. 152, A, B). 



2. In the cytoplasm of the cell they grow into the large rounded 

 schizonts, distinguished by the absence of reserve food-materials in 

 their cytoplasm, and by the large vesicular nucleus with a karyosome 

 (Fig. 152, B). 



In a few rare instances namely, Coccidium mitrarium, Lav. et Mesn., 

 Cryptosporidium muris, Tyzzer, and the recently-described Sdenococcidium 

 intermedium (see p. 351, infra), the trophozoite is free as in gregarines. In 

 Barroussia spiralis, from Cerebratulus sp., the schizont during its early phases 

 of growth is vermiform and spirally twisted, but becomes rounded off when 

 full grown (Awerinzew, 47). In the intranuclear parasite of the mole, Cydo- 

 spora caryolytica, the schizonts are stated by Schaudinn (147) to be sexually 

 differentiated, as also the merozoites to which they give rise. In the case oi Addea 

 ovata, however, a sexual differentiation of the schizonts alleged by Siedlecki 

 (Fig. 163) is stated by Schellack and Reichenow to be due to a confusion of two 

 distinct species ; the supposed microschizonts, giving rise to microgametocytes, of 

 Siedlecki, are stated to be in reality the schizonts of Barroussia alpina, Leger, 

 while Siedlecki's macroschizonts alone represent the true schizonts of Addea 

 ovata; compare also Debaisieux. Chagas, however, describes in Addea 

 hartmanni (Chagasia hartmanni, Leger, 644) distinct male and female genera- 

 tions, microschizonts and macroschizonts, multiplying by microschizogony 

 and macroschizogony respectively. 



3. In the full - grown schizont (agamont) the nucleus divides 

 repeatedly by binary fission (Fig. 51, p. 106 ; Fig. 152, C, D, E) 

 until a variable number of nuclei, about thirty or forty as a rule, 

 are produced. The body of the schizont then divides into as many 

 segments as there arc nuclei, leaving a certain quantity of residual 

 protoplasm, and each segment becomes a merozoite (" schizozoite," 

 Leger). 



The schizogony takes place without any formation of resistant membranes 

 by the parasite, but the remains of the host-cell may furnish an envelope or 

 cytocyst within which the multiplication of the parasite proceeds. As a general 

 rule the merozoites produced are arranged like a barrel round the residual 

 protoplasm (Fig. 153, F), forming a so-called corps en barillet. In Caryo- 

 tropha a double process of schizogony occurs, recalling somewhat that of 

 Porospora; the schizont divides into a number of cells, " schizontocytes " or 

 " cytomeres," each of which divides in its turn into a cluster of merozoites 

 arranged in a corps en barillet. 



The nuclear multiplication in the schizont is not always effected by simple 

 binary fission, as in Coceidium schubergi. In Addea ovata binary or multiple 

 fission of the nucleus occurs (Jollos). First the centriole contained in the 

 karyosome, and then the karyosome itself, divides into two ; the whole nucleus 

 may then divide into two also, or the division of the karyosome may be re- 

 peated several times, until the nucleus contains a number of karyosomes. 

 In the later nuclear divisions the karyosome becomes very small, consisting 

 of little more than the bare centriole, while the peripheral chromatin increases 



