218 PROTOZOAN PARASITISM 



It is essential to an understanding of it to realize 

 that the usual course of life is asexual but that periodi- 

 cally certain of the young organisms become differ- 

 entiated into males and females and these conjugate 

 to give a sexual cycle, presumably rejuvenating the 

 race. 



In reference to the accompanying diagram, which 

 represents both cycles as they occur in a typical 

 species which inhabits the epithelium of the intestinal 

 mucosa, a graphic description of the scheme will be 

 attempted in as simple terms as possible. 



Starting with (1), the young coccidium, a minute 

 ovoid organism within an epithelial cell, we see the 

 parasite grow to a size where it practically occupies 

 the whole housing cell, the cytoplasm of this cell being 

 fed upon and the nucleus crowded and flattened to 

 the bottom. This large asexual individual is called 

 a Schizont (2). As it grows larger its nucleus di- 

 vides and by repeated division becomes of a number 

 characteristic of the species (3). The cytoplasm 

 then splits (4) into as many new individuals as there 

 are nuclei, this process of division being known by 

 the term Schizogony. These young offspring are 

 elongated cycle-shaped or wormlike bodies, called 

 Merozoites. They are actively motile and their 

 housing cell is burst (5) leaving the remnants of 

 it and the parent Schizont. These Merozoites wig- 

 gle actively about and penetrate other host epithe- 

 lial cells (6), in which they become rounded and 

 from which point the asexual process of maturition 



