COCCIDIA 



569 



(merozoites) developed after asexual schizogony spread the infection 

 within the same host (auto-infection), while the sporozoites formed 

 after sexual reproduction may spread the infection to a new host. 



The life cycle of a coccidium may, therefore, be outlined as follows 

 (Doflein, Schaudinn) : A cyst containing sporozoites, the product of 

 sexual propagation, is taken into the gastro-intestinal tract of an animal. 



FIG. 198 



Life cycle of Coccidium schubergi. (After Schaudinn.) Sporozoites penetrate epithelial 

 cells and grow into adult intracellular parasites (a). When mature the nucleus divides re- 

 peatedly (6), and each of its subdivisions becomes the nucleus of a merozoite (c). These enter 

 new epithelial cells, and the cycle is repeated many times. After five or six days of incuba- 

 tion the merozoites develop into sexually differentiated gametes; some are large and well 

 stored with yolk material (d, e, f ) ; others have nuclei which fragment into many smaller par- 

 ticles ("Chromidia"), each granule becoming the nucleus of a microgamete, or male cell (d), 

 h, i, j). The macrogamete is fertilized by one microgamete (0), and the copula immediately 

 secretes a fertilization membrane, which hardens into a cyst. The cleavage nucleus divides 

 twice, and each of the four daughter nuclei forms a sporoblast (k) in which two sporozoites are 

 produced (I). 



The cyst wall or membrane is dissolved, the sporozoites become free, 

 and a number of them enter epithelial cells, penetrate into their 

 nuclei, and grow into forms, which in some coccidia already show a 

 differentiation into cells that will later furnish the male and others 

 that will furnish the female gametes. Both kinds of cells then divide 

 asexually and form male and female gametes, respectively. These 



