IT 



PHYLUM PROTOZOA 



87 



which they were derived. This multiplication may take place on such an 

 extensive scale that the epithelium may be partially or completely destroyed. 

 It is only, apparently, when such extensive damage has been done, or is 

 threatened, that multiplication by sporogony takes place the invasion of a 



Fio. 66. Life-history of Coccidium schubergi. a. penetration of epithelium cell of host 

 by sporozoite ; b-c, stages of multiple fission (schizogony) ; d, gametocyte ; e,f, formation of 

 megagamete (ovum) ; g, fertilisation ; h, j, formation of microgametes (sperms) ; It, 

 development of fertilised ovum into four spores ; I, formation of two sporozoites (falciform 

 young) to each spore. (From Calkins, after Schaudinn.) 



new host being by this process rendered probable, and the continuance of the 

 race being thus provided for in the event of the death of the host in which the 

 epithelium has become destroyed. In this process certain of the merozoites, 

 instead of developing into trophozoites, grow more slowly (d), and become 



