THE LIFE CYCLE 575 



grows into a somatella of about sixty-four cells, in a rhythm of repeated 

 mitoses. 



Then follows the third asexual reproduction, in which the organism 

 divides by plasmotomy into motile unicellular spindle-shaped merozoites, 

 similar in size and pattern to the sporozoites. These in turn infect other 

 intestinal epithelial cells, and this phase of the cycle is repeated an un- 

 known number of times so long as susceptible host cells are available 

 for infection. This phase ends the asexual part of the life cycle, as 

 gametogenesis approaches, except in the male. 



The sexual phase is marked by developing sexual dimorphism among 

 the merozoites. Presumably sex is determined at fertilization, and all 

 functional individuals derived from one zygote will accordingly be of 

 one sex only, and the myriapod host must have acquired an infection by 

 spores of each sex, in order that both male and female gametes of 

 Eimeria, fertilization, and spore formation may ensue in the intestine. 

 The sexual dimorphism of the gametocytes is determined by two factors, 

 the metabolic rate and probably also the chemical nature of the food 

 reserves on the one hand, and the structure and number of gametes pro- 

 duced on the other. Both male and female gamete mother cells grow 

 to the size and spherical form of the trophozoite, but do not run its 

 type of rhythm of cleavage, mitoses, and plasmotomy. The female is 

 early differentiated from the male by the internal elaboration of spheri- 

 cal granules of food reserves or yolk, whereas in the male none appear. 

 This functional and structural dimorphism is accompanied by a differ- 

 ence in nuclear behavior. In the male there appear to be as many as six 

 successive mitoses, as in the trophozoite, producing up to sixty-four 

 gametes. These are elongated slender, deeply staining bodies, largely 

 of nuclear substance, with one trailing flagellum and a second one lat- 

 erally attached to the anterior half of the body and free posteriorly. 



The female gamete mother cell, on the other hand, undergoes no divi- 

 sions, and transforms directly into the Qgg, though indications of metab- 

 olic activity appear in deeply staining spherules adjacent to the parasite 

 in the host's cytoplasm. This absence of divisions in the female gameto- 

 cyte, and their superabundance in the male, not only emphasizes a 

 metabolic contrast, but also on cytological grounds offers cytological 

 difficulties to the existence of maturation in these phases. These ob- 

 stacles, which Schaudinn (1900) left unresolved, were removed by the 



