292 Sporozoa 



volves a preliminary arrangement of nuclei at the surface of the schizont 

 and then a superficial budding (Fig. 6. 13, A). However, the trophozoite 

 of Caryotropha (Fig. 6. 13, B-D) first divides into cytomeres (meroblasts) 

 and each meroblast then produces merozoites. 



There appears to be a limited number of merogonic cycles, the exact 

 number varying with the species — usually two in Adelina deronis (43); 

 three in Eimeria separata and E. miyarii; and foin- in E. Jiieschidzi of rats 

 (118). The time required for completion of the first merogonic genera- 

 tion, as reported for different species, ranges from about 25 hours to 25 

 days. 



The last generation of merozoites produces two types of gametocytes, 

 which vary in relative numbers. In Adelina deronis, in which the gameto- 

 cytes develop in syzygy and relatively few microgametes are produced, 

 there are about twice as many microgametocytes as macrogametocytes 

 (43). In Eimeria nieschuhi, which produces many microgametes, macro- 

 gametocytes outnumber microgametocytes about three to one (118). The 

 mechanism underlying the differentiation of two kinds of gametocytes is 

 not yet known. However, the development of a normal cycle in the host 

 after experimental introduction of one oocyst (135) suggests that the 

 basic sexual differentiation occurs early in development of the zygote, 

 although its expression may be delayed until gametocytes appear. 



The gametocytes may be similar in size (Eimeriida) or the m.acroga- 

 metocyte may be distinctly the larger (Adeleida). The macrogametocyte, 

 during development, typically accumulates stored reserves such as the 

 glycogen in Eimeria tenella (30), Avhereas the microgametocyte contains 

 little stored food. The gametocytes of Eimeriida differentiate independ- 

 ently, and the microgametocyte typically produces many microgametes 

 (Fig. 6. 13, E-G). In the Adeleida the two types of gametocytes, sometimes 

 at an early stage of development, become associated in syzygy (Fig. 6. 

 13, H, I), which is correlated with the production of relatively few, often 

 2-4, microgametes (Fig. 6. 13, J). For the Coccidia as a group, the mor- 

 phological differentiation of macrogametes and microgametes is marked 

 and the production of small flagellate microgametes (Fig. 6. 13, K) is 

 typical. Microgametogenesis in Eimeriida generally resembles the process 

 described for Ovivora thalassemae (Fig. 6. 13, E-G). In Merocystis (105) 

 and Myriospora (82), however, the microgametocyte divides into gameto- 

 blasts, each of which produces a number of microgametes. The details of 

 syngamy seem to be similar throughout the group. 



Either before or immediately after entrance of a microgamete the 

 macrogamete usually secretes an oocyst membrane, although the zygote 

 of the Haemogregarinina is at first a migratory ookinete which later 

 secretes a thin flexible membrane. In the majority of Coccidia, the oocyst 

 membrane is relatively thick and firm, and may be composed of two or 



