390 ch-^lEles h. swift 



This rapid increase in size of the cords accounts for the more 

 rapid growth of the embr\'onic ovan'. 



This last criterion is of less weight than the preceding, and 

 is of importance only when used in connection with the others. 



THE EVOLUTION OF THE SEXUAL OR SEMIXIFEROUS CORDS OF 



THE e:mbryoxic testis 



The next three embn.-onic stages studied, namely, 7, 8; and 

 9 days, may be described together, since they are characterized 

 in common by the same facts, and the changes although oc- 

 curring, are not abrupt or great. 



During this period the sex of the indi\'idual can be easily 

 ascertained, either with or without the aid of the microscope. 

 In the latter case the first criterion mentioned above, relative 

 size of the gonads, is amply sufficient, and with the microscope 

 a single glance at the germinal epithelium, the sexual cords, 

 and the number of primordial germ-cells in the epithelium is all 

 that is needed. 



Both testes are slowly increasing in size but in all cases the 

 left is found to be the larger. They are becoming rounder and 

 in the process the broad connection with the Wolffian body is 

 being narrowed: in other words, the}' are being constricted or 

 pinched off of the Wolffian body. 



The germinal epitheUum is reduced to a single laj'er of cu- 

 boidal cells, and by the end of this period of 7 to 9 days of de- 

 velopment, all connection with seminiferous cords is severed. 

 This is brought about by a condensation of the mesenchj-me 

 imder the epithelium to form the tunica albuginea. 



The seminiferous cords, which will in the future claim most 

 of our attention, make up the greater part of the testis. They 

 have a definite orientation from the epithehimi obliquely toward 

 the narrowing attachment of the testis with the Wolffian body.' 

 Each cord is, of course, not entirety straight, but wav}'. They 

 are separated one from another by a verj' thin layer, one might 

 almost sa3' fihn, of stroma and a number can be followed at one 

 time across the field of the microscope. 



