SEX-CORDS AND SPERMATOGONIA IN CHICK 389 



Wlien the embryo chick has reached the 156th hour of devel- 

 opment (6^ days), the formation of cords of first proUferation 

 ceases rather abruptly, and about this time it is possible to 

 determine the sex of the individual. 



In determining the sex of the embryo there are several cri- 

 teria which are of value. 



1. The relative size of the gonads. It has been known for 

 a long time that the left gonad in the female grows rapidly while 

 the right does not, so that in a short time after sexual cord for- 

 mation, the left gonad or ovary has far outgrown the right. In 

 the case of the male individual both gonads continue to grow. 

 This criterion is of value, but too much reliance can be placed 

 upon it especially during the 6th day, for in all cases, male as 

 well as female, the left gonad is the larger. The left gonad is the 

 larger during the indifferent stage and in the male is the larger 

 even in the adult (Etzold, '91). 



2. Thickness of the germinal epithelium. This and the fol- 

 lowing criterion I believe to be the most important. In the 

 male the germinal epithelium is thin at the end of sexual cord 

 formation and continues so, while in the female the germinal 

 epithelium over the left gonad or ovary still consists of the sev- 

 eral layers of columnar cells. In the male the epithelial cells 

 become very quickly a single layer in thickness and the indi- 

 vidual cells cuboid in character. This is an excellent test. 



3. Number of primordial germ-cells in the germinal epithe- 

 lium. In the germinal epithelium of the left female gonad the 

 number of primordial germ-cells appears undiminished, while in 

 the epitheliimi covering the male gonads there is hardly a single 

 one to be seen (Hoffman, '92 and Swift, '15). In the case of 

 the male they all appear to have gone into the sexual cords, and 

 in the female to be remaining quiescent until the formation of 

 the cortical cords, in the evolution of which they play so im- 

 portant a role (Swift, '15). 



4. Attachment and growth of the sexual cords. The cords 

 remain thin and attached to the germinal epithelium for a long 

 time in the male gonad, while in the female they increase rap- 

 idly in diameter and become detached early in their evolution. 



