Origin of Sexuality 277 



same adult, can fuse to constitute close fertilization, or whether 

 individuals from distinct adults only fuse, is still undetermined. 

 The conjugate mass then starts a spore-forming generation. 



In the genus Stylorhynchus two adults also encyst, but one 

 of them becomes di\dded up into male gamete cells, each of 

 which forms a flagellate tail and pointed head. The other 

 divides up into smaller cells that remain passive. Then the 

 larger motile male gamete cells penetrate the adjoining cavity 

 that contains the smaller gametes, and union in pairs takes 

 place. 



In Pterocephalus one of the two adults in a cyst breaks up 

 into numerous small attenuate chromatin bodies or spermat- 

 ozoids, each bearing a posterior flagellum. The other breaks 

 up into large eggs with abundant stored food. The latter, 

 remaining passive, are fertilized by the motile male cells. 



The subdivision Coccidese includes Coccidium in which the 

 sexual stage has been fully traced. Here the adult cells, at 

 an early period in sex differentiation, become recognizable 

 as male and female cysts, since the former become filled with 

 fijiely granular, the latter wdth coarsely granular, materials. 

 The chromatin substance of the nucleus in the male cyst, 

 derived mainly from the nucleolus, flows out along radiating 

 threads into the peripheral part of the protoplasm, and forms 

 small chromatin granules that unite, elongate, and along with 

 the protoplasm form each an anterior and posterior flagellum. 

 The spermatozoids or microgametes thus formed then escape. 

 The probability further is — judging from like cases — that 

 chromatin material is excreted before the above granules unite 

 to form the male chromatin masses. The future female cysts 

 produce each one egg, and during the process the nucleolar 

 chromatin is largely or wholly extruded. The enucleolated 

 nucleus then matures, shows chromatin granules in its sub- 

 stance, and at length travels to the surface of the now ripe 

 egg. "Here a 'cone of reception' is formed as a little prom- 

 inence of clear hyaline protoplasm, from wliich a thin streak 

 of similar substance extends as far as the nucleus. A micro- 

 gamete touches the cone and adlieres to it The cone of recep- 



