TELOSPOKIDIA. 51 



individuals as the number of nuclei. This process of multiple 

 j&ssion may be an asexual process {schizogony), and the resulting 

 daughter individuals (merozoites) will grow into adult tropho- 

 zoites, or the daughter individuals may all be gametes. In 

 the former case also, after schizogony has been repeated 

 a number of times, some of the merozoites develop into 

 gametocytes, which give rise to gametes. The gametes 

 conjugate, the process being known as syngamy, and form 

 zygotes. The zygote then becomes enclosed in a resistant 

 cyst, known as the oocyst. Inside the oocyst the zygote 

 may either divide directly into a number of motile vermiform 

 bodies called sporozoites, or the zygote may &st divide into 

 separate bodies called sporoblasts, which become encysted in 

 secondary cysts known as sporocysts ; within each sporocyst 

 the sporoblast gives rise to a number of sporozoites and 

 a residual body. The mature oocyst of this latter type thus 

 contains a number of sporocysts, each containing many 

 sporozoites. 



The infection of a new host is brought about by the con- 

 taminative or inoculative method, and the sporozoites seek 

 their way to the particular type of cell which they usually 

 parasitize, viz., an epithehal cell (Gregakinida, Coccidia) 

 or a blood-corpuscle (H^mosporidia) . The adult forms of 

 CrREGARiNiDA are invariably extracellular or lumen dwelHng, 

 young growing stages alone being intracellular. Adult forms 

 of Coccidia and H^mosporidia are persistently intracellular, 

 young, adult, and reproductive phases all occurring inside 

 ahost-cell. In the majority of Gregarinida (Eugregarinaria), 

 the sporozoite grows directly into a gametocyte which produces 

 gametes. In the Schizogregarinida schizogony also takes 

 place. In the Coccidia and H^mosporidia regular alterna- 

 tion of the asexual method or schizogony, and the sexual method 

 or sporogony, is the rule, and this alternation of generations 

 frequently takes place in two distinct hosts. In Gregarinida 

 and the H^mosporidia the sporozoites are formed directly 

 by divisions of the zygote ; in Coccidia the zygote encysts 

 and divides into sporoblasts which become sporocysts, and the 

 oocyst thus contains a number of sporocysts, inside which the 

 sporozoites are developed. When sporocysts are present, 

 the oocyst is termed sporocystid, and, according to the 

 number present, is described as disporocystid, tetrasporocystid, 

 or poly sporocystid. The sporocysts are described as monozoic, 

 dizoic, tetrazoic, octozoic, etc., according to the number of 

 sporozoites present in each. 



The subclass is divided into three orders, as follows : — 



Mature trophozoite extracellular, large ; 



zygote non-motile ; sporozoites within [em. Doflein, p. 52. 



a spore Gregarinida A. Schneidei*, 



e2 



