6 SPOROZOA. 



or contractile filaments which bring about contortions of the 

 body. The sarcocyte may run inward as one or more septa 

 and thus divide the body into a number of apparent segments : 

 in the cephahne Gregarines (fig. 30) the body is thus seen to 

 consist of three segments, known respectively as the epimerite, 

 protomerite, and deutomerite. Sometimes the organisms may 

 attach themselves to each other and form clusters or linear 

 chains, termed syzygies. The endoplasm is usually granular, 

 and contains sorted-up food material in various forms. The 

 nucleus is usually very large, spherical, and vesicular in type, 

 with one or more distinct karyosomes. 



Reproduction. — Like other parasites, Spokozoa possess the 

 power of prohfic multiphcation as a necessary adaptation for 

 the maintenance of the species. Both asexual and sexual 

 methods are known in all groups. Asexual reproduction may 

 be by binary fission (as in Babesia), by multiple fission (as in 

 CocciDiA and H^mospokidia), or by budding, which may be 

 exogenous (as in Myxosporidia) or endogenous (as in certain 

 Schizogregarines). The trophozoite when it is about to enter 

 on asexual reproduction is known as a schizont (or agamont), 

 the process being termed schizogony (or agamogony) and 

 the resulting products of division being termed merozoites. 

 Sexual reproduction [syngamy) is by isogamous or anisogamous 

 conjugation or sometimes by the fusion of sister individuals 

 derived by fission of the same parent cell or nucleus {autogamy). 

 Trophozoites which associate with one another for the purpose 

 of sexual reproduction are designated as sporonts or gametocytes, 

 which may differ from one another and are then known as 

 microgametocytes and macrogametocytes, according as they give 

 rise to males or microgametes and females or macrogametes. 



The fusion of two gametes results in the formation of 

 a zygote which, when activelj^ motile and vermiform (as 

 in H^mosporidia), is generally knoAvn as an ookinete. 

 The zygote maj^ secrete a distinct membrane round itself 

 and become a passive spherical body known as an oocyst. 

 Cellular division of the protoplasm within the oocyst gives rise 

 to the formation of a number of sporoblasts, each of which 

 becomes surrounded by a wall, the sporocysf, and is then 

 known as a spore. Inside a spore are developed a smaller 

 or larger number of minute germs or sporozoites which are 

 the infective bodies, and start the cycle again. These various 

 stages, starting from the zygote and leading to the formation 

 of the spores and sporozoites, constitute sporogony. Asexual 

 and sexual methods of reproduction regularly alternate in the 

 life-cycle of the majority of forms, and compHcated hfe-histories 

 result. In such cases schizogony takes place usually in the body 

 of one host and gametogony and sporogony in the body of 

 an animal belonging to a widely different group. The former 



