THE URINOGENITAL SYSTEM 



395 



(3) larger size of the left ovary and ultimate disappearance of the 

 right one; (4) behavior of the stroma, particularly the albuginea. 

 The sex of the embryo can first be definitely determined about 

 the 156th hour, by the relative sizes of the two gonads, by the be- 

 havior of the germinal epithelium and by the presence of a larger 



K,'-^ 





germ. ep. 



pro. 



m. 



y^''^/. 





4 



coelom 



.fSf- 









Fig. 227. — Portion of a transverse section through an 

 ovary of a 6^ day chick embryo (after Swift), germ, 

 ep., germinal epitheHum. m. c, sexual cord. pr. o., 

 primordial germ-cells. 



number of primordial germ-cells in the germinal epithelium of 



the female. (Swift.) 



As already stated, the sexual cords form the seminiferous 

 tubules of the testis; they are made up of two kinds of cells, viz.: 

 the primordial germ-cells and the ordinary peritoneal cells derived 

 from the germinal epithelium. After the seventh day they con- 

 stitute most of the bulk of the testis, and the rete cords are pressed 

 towards the hilum by the sexual cords which radiate in that direc- 



