364 The Aninial Kingdom 



In preparation for sexual reproduction, some of these merozoites 

 after invading the host cell become gametocytes instead of trophozoites. 

 Some of these enlarge to become individual macrogametes, while others 

 divide to form microgametes. The fusion of a macrogamete with a 

 microgamete produces a zygote. The zygote secretes a heavy wall 

 about itself and escapes into the lumen of the bile duct. Here it be- 

 comes an oocyst which passes from the rabbit with the feces. Within 

 the oocyst four spores, each with two sporozoites, are developed. This 

 process of spore formation is sporogony. If the oocyst is ingested by 

 another rabbit, each sporozoite is able to invade a host cell and de- 

 velop into a new trophozoite. In this way, the infection spreads rapidly 

 from one individual to another. 



ASEXUAL CYCLE 



TROPHOZOITE 



VOUNG SCmZONT. 

 EPITHELIAL CELL 



SEXUAL CYCLE 



AMETOCYTE 



MATURE OOCYST 



Fig. 116. — Life history of the sporozoan Eimeria stiedae. 



Other species of Eimeria parasitize chickens, turkeys, dogs, cats, 

 cattle, rats, and mice. In both rabbits and poultry, coccidiosis causes 

 a large number of deaths in the young. The best methods of control 

 involve careful sanitation of the living quarters. 



