104 PHYLUM PROTOZOA—THE SIMPLEST ANIMALS. 
oval or spherical cell with a nucleus. It lives a quiescent 
life within the host cell, growing and absorbing nourishment 
until the resources of the cell are exhausted. 
Life history.—The coccidium enters the host cell as a 
minute sickle-shaped body, pointed at the anterior end, and 
Fic. 47.—Life history of Coccidium.—After Schaudinn. 
1. Sporozoite; 2. Sporozoite entering a cell and becoming a trophozoite ; 
3-4. Schizont, forming merozoites; 5. Merozoites entering another 
cell; 6°. Merozoite forming macrogamete; 6%. Merozoite forming 
microgametes ; 7. Free microgamete ; 8-9. Fertilisation of macrogamete 
by microgamete; 10. Zygote within odcyst; tx. Formation of spores 
within odcyst ; 12. Spores forming sporozoites. 
more blunt posteriorly. This is the spovozoite stage of the 
life history; it is liberated from a cyst (odcyst) when the 
latter is swallowed by the centipede in its food. When 
freed in the gut the sporozoite progresses by forward gliding 
movements, alternating these by flexions, bending itself like 
