924 SUMMARY OF CURRENT RESEARCHES RELATING TO 



(Fishes, Amphibians, Eeptilcs, Birds, and Mammals) ; and deduces the 

 following ptncral conclusions : — 



(1) AVith a few differences, conditioned by the structural level of the 

 testes, the spermatogenesis of Vertebrates exhibits a constant type. 



(2) In Mammals, Birds, and Reptiles, there is some division of 

 labour, for the spermatoblasts i)roduce not only spermatozoa, but also 

 elements destined for the expulsion and nutrition of the essential pro- 

 ducts. In Amphibians and Selachians, the spermatoblasts form only 

 spermatozoa, expelled by the proliferation of the germinal cells. 



(3) The Amphibian spermatogenesis is a median type ; a spermatic 

 cyst in the canal of an Amjihibian corresponds morphologically to an 

 ampulla in the Selachian testes. 



(4) The germinal cells, the fixed cells of Sertoli, the " cellules do 

 soutien " of Merkel, represent the matrix of the spermatic eiJithelium, 

 giving origin to the new spermatoblasts. 



(5) Following Fkmming, the author regards as cellular what other 

 investigators describe as nuclei — the elements, namely, which divide to 

 give origin to the spermatoblasts. 



(0) The protoplasmic network described by various authorities as 

 originating from the germinal cells and extending between the elements 

 of the testicular canal, is the result of the action of the nuclei of the 

 dividing spermatoblasts. 



(7) In Mammals, Birds, and Eeptiles, the expulsion of the sperma- 

 tozoa is favoured by the secretory modification of some of the elements 

 of the canal. In Amphibians and Selachians the expulsion is referable 

 to the proliferation of the germinal cells. 



(8) The spermatozoa arise directly from small nuclear asters, and 

 are eqiiivalcnt, therefore, not to cells, but to nuclei. Both chromatic and 

 achromatic portions of the spermatozoa have nuclear origin. Only in 

 Mammals were two different kinds of spermatozoa to be observed. 



(9) The polymorphic nuclei, as yet described only in Amphibians, 

 occur throughout the Vertebrate series. 



(10) The physiological regeneration of the epithelium of the canals 

 occurs from the germinal cells, when all the elements produced by the 

 first generation have been expelled. There is a constant relation between 

 the transformation of the spermatoblasts and the proliferation of the 

 germinal cells. 



Spermatogenesis of Reptiles.* — Dr. A. Prcnant has studied the 

 spermatogenesis of reptiles in Gecko communis, Anguis fragilis, Laccrfa 

 agilis, and Vipera aspis, but especially in the first named. 



(1) Spermatogonia, seminiferous, or germinative cells. In these cells 

 the author has especially studied the granular crescent in the protoplasm 

 which forms the "Kebenkern," and has observed the presence of that 

 element itself. 



(2) Nematoblasts and Spermatozoids. The nematoblasts exhibit the 

 "Nebenkern." It forms amid a crescent of granules. Its history seems 

 to be that as it becomes differentiated it gains the anterior pole of the 

 nucleus, there becomes less definite, and along with the surrounding 

 protoplasm forms a head-cap. The crescent of granules appears to give 

 rise also to the caudal knob and to the beginning of the caudal filament. 



* La Cellule, iv. (188S) pp. 181-97 (1 pi.). 



