128 



PHYLUM PROTOZOA — THE SIMPLEST ANIMALS 



arrange themselves around the periphery of the cell, whilst 

 the protoplasm breaks up to form along with them bodies 

 of a shape similar to the sporozoites. There are important 

 structural differences, however, apart from the difference in 

 origin. The parasites, now known as merozoiteSy rupture 



Fig. 58. — Life-history of Coccidium. — After Schaudinn. 



I. Sporozoite ; 2. Sporozoite entering a cell and becoming a trophozoite; 

 3-4. Schizont, forming merozoites ; 5. Merozoites entering another 

 cell ; 6a. Merozoite forming macrogamete ; 6b. Merozoite forming 

 microgametes; 7. Free microgamete ; 8-9. Fertilisation of macrogamete 

 by microgamete ; 10. Zygote within oocyst ; 11. Formation of spores 

 within oocyst ; 12. Spores forming sporozoites. 



the host cell, move in the gut cavity after the manner of the 

 sporozoites, enter fresh epithehal cells, and repeat the fore- 

 going cycle until ultimately the greater part of the gut 

 epithelium is destroyed. In about five days, however, 

 owing perhaps to the failing capacity of the host to nourish, 

 the limit of asexual reproductivity is reached, and the 



