384 EMBRYOLOGY. 



communication with them, but only after the maturation of the 

 seminal filaments begins. 



Many differences of opinion still prevail concerning the development 

 of the testis in the higher Vertebrates. It is true that the presence of 

 a germinal epithelium upon the surface of the mesonephros has also 

 been established in this case by WALDEYER for the male, but its 

 participation in the fundament of the testis has been called in 

 question. According to the original account of WALDEYER, which 

 is still defended by many investigators, especially by KOLLIKER, the 

 seminal tubules are morphological products of the primitive kidney. 

 However, more recent researches, which it must be admitted do not 

 yet harmonise with one another in all points, indicate that the 

 development of the testis of Reptiles, Birds, and Mammals agrees 

 with that of non-amniotic Vertebrates in the main outlines. In 

 continuation of the work of BORNHAUPT and EGLI, who it is true 

 worked with incomplete methods of investigation, BRAUN has recently 

 maintained for Reptiles, SEMON for the Chick, MIHALKOVICS and 

 JANOSIK for the latter and for Mammals, that in the male also the 

 germinal epithelium begins to proliferate, penetrates into the depths 

 of the testis, and furnishes the primitive seminal cells. The tubules, 

 which according to KOLLIKER and WALDEYER grow into the funda- 

 ment of the testis from the primitive kidney, the sexual cords, 

 serve only for carrying away the semen. As stated by BRAUN for 

 Reptiles, and by SEMON for the Chick, they sprout out from the 

 epithelium of Malpighian corpuscles, as in the case of the Amphibia. 



Although according to these accounts the double origin of the 

 substance of the testis, on the one hand from the germinal epithelium, 

 on the other from the primitive kidney, can no longer be well! 

 called in question, nevertheless in the details many conditions, 

 which are still differently described in the higher Vertebrates, 

 demand renewed investigation. Before all else this point should be 

 still further explained : In what proportion do the epithelial cells 

 furnished by the germinal epithelium and those by the primitive 

 kidney share in the formation of the testicular substance ? Are the 

 tubules which produce the semen formed exclusively from germinal 

 epithelium, or is it only the seminal mother-cells which have this 

 origin, while there are associated with the latter indifferent cells from 

 the " sexual cords of the primitive kidney " ? 



I hold it to be the more probable that the tubules producing the semen, 

 the tubuli seminiferi, are derived from the germinal epithelium; the tubull 

 recti and the rete testis, on the contrary, from the primitive kidney. 



