THE SPOROZOA 223 



Haemosporidia. When the merozoites are very numerous they may be 

 disposed in a double series. The remarkable form parasitic on Polymnia, 

 recently described by Siedlecki [55tt] under the name Caryotropha 

 mesnilii, presents an interesting divergence from the usual type of 

 schizogony. The schizont divides first into ten or fifteen large rounded 

 cells, termed by Siedlecki schizontocytes (Fig. 67). Each schizontocyte 

 then gives origin to twenty or thirty merozoites, so that the host-cell 

 finally contains not one but many "barillets" (Fig. 67, rf). This method 

 of schizogony recalls the formation of spores in Porospora (see above, 

 p. 188), and is also interesting for its relation to the formation of the 

 gametes (p. 225). 



In Coccidium schubergi and most other Coccidia the schizonts 

 show no trace whatever of sexual differentiation until the final 

 term of the schizogony, when they become gametocytes of two 

 kinds, distinct from one another and from the ordinary schizonts. A 

 most important variation of this type is seen in Adeka ovata (Fig. 55) 

 and some other species, where the trophozoites formed from the 

 sporozoites exhibit sexual characters from the outset, and can be dis- 

 tinguished as male or female, but multiply asexually through many 

 schizogonous generations before finally giving rise to gametes. An 

 extreme case of sexual differentiation during schizogony is seen, 

 according to Schaudinn [5 la], in Cyclospora caryolytica from the 

 mole, where no differentiation can be observed in the sporozoites 

 themselves, but is discernible in the trophozoites produced from 

 them after one hour's growth. The female schizonts of Cyclospora 

 have coarsely alveolar cytoplasm of very fluid consistence, and 

 without any reserve substances. The male schizonts are charac- 

 terised by the possession of strongly refractile, pigment-like granules. 

 The merozoites produced from the two classes of schizonts also 

 differ markedly both in character and arrangement. The female 

 gametocytes have a coarsely alveolar cytoplasm packed with 

 large granules of reserve material resembling yolk, while the 

 male gametocytes are distinguished by cytoplasm which is ex- 

 tremely finely granulated and stains very readily. In this 

 species, therefore, four distinct classes of trophozoites can be 

 distinguished. 



In some Coccidia for example, Adelea ovata, A. mesnili, Eimeria 

 nova, and Klossia kelicina the number of microgametes produced 

 from a microgametocyte is not indefinite, but constantly four only. 

 This reduction in the number of microgametes is usually correlated 

 with a precocious association of the gametocytes, a condition re- 

 sembling that which is commonly seen in Gregarines. Thus in A. 

 uvata the macrogametocytes when full-grown fall out of their host- 

 cells and pair with microgametocytes, which may be not full-sized. 

 The two cells adhere together, and the female cell undergoes 

 maturative changes, becoming a macrogamete, while the micro- 



