SEX-CORDS AND SPERMATOCJONIA IN t'HK'K 407 



material in the mitochondrial portion of the mitochondrial 

 crescent, but I am very certain that the attraction-sphere and 

 its surrounding body of mitochondria ought not to be called the 

 yolk nucleus of Balbiani for it does not have a nuclear origin. 



The denser ground substance in the mitochondrial portion of 

 the mitochondrial crescent may be derived from the nucleus 

 and fall into the class of a true yolk nucleus or a chromidial sub- 

 stance in the sense of R. Hertwig. 



It may be that the mitochondrial portion of the mitochondrial 

 crescent plays a role in the oocyte in the formation of vitellus, as 

 has been suggested, acts as a true 'couche vitellogene; ' but as to 

 its function in the male, I cannot even surmise. 



SUMMARY 



1. In the male chick the true sexual cords or seminiferous 

 cords originate from the germinal epithelium during the sixth 

 and seventh days of development and are the result of localized 

 activity of the epithelium. Nearly all the primordial germ-cells 

 present in the germinal epithehum are carried down into the 

 seminiferous cords but they play only a passive role for at this 

 time they show no evidences of cell division. 



2. The sexual cords remain attached to the germinal epithe- 

 lium for only a short time, and continue to grow, after formation 

 of the albuginea, as a result of division of the peritoneal cells. 



3. At the end of the seventh day of development the sex of 

 the individual can be easily told, for in the male the gonads are 

 of nearly equal size, while in the female the left gonad is much 

 the larger. In the male the germinal epithelium remains thin 

 after the formation of the sexual cords and contains very few- 

 primordial germ-cells, while in the female the epithelium of the 

 left gonad or ovary continues to be thick and contains many 

 primordial germ-cells. 



4. During the eighth and ninth days of development the 

 gonads increase slowly in size and the thin sexual cords make up 

 most of the volume of the testes. They are separated from one 

 another by a thin layer of stroma and have a definite orienta- 

 tion from germinal epithelium obliquely down towards the 



