210 



NORMAL HISTOLOGY. 



developing spermatozoa, embedded within the inner end of the 

 supporting cell of Sertoli. 



Spermatogenesis varies among the different classes of vertebrate 

 animals ; the account here given refers to man and the higher 

 mammals. 



The originally round spermatids promptly exhibit a tendency to 

 elongate and to become pyriform ; several such cells, with partially- 

 formed spermatic filaments, are often crowded together by the pressure 

 of the surrounding elements, and, in consequence, come to lie in 

 close relation and in intimate union with the centrally projecting 

 protoplasm of the sustentacular cells. Such appearances, probably 



FIG. 253. 



FIG. 254. 



Section of testicle of musk-rat, ex- 

 hibiting early stage of spermatogenesis : 

 a, membrana propria ; 6, zone of pari- 

 etal cells ; c, mother-cells ; d, sperma- 

 toblasts developing into spermatozoa. 



Section of testicle of musk-rat, showing 

 later stage of spermatogenesis : a, mem- 

 brana propria ; b, zone of parietal cells ; c , 

 mother-cells ; d, fan-shaped masses of ele- 

 ments concerned in producing spermato- 

 zoa (e). 



partly the result of mechanical forces, at present are regarded as 

 indicating an important role on the part of the sustentacular cells 

 in the production of the spermatozoa, an assumption seemingly 

 warranted by recent investigations. Coincidently with the changes 

 in the general form of the spermatoblasts, the nuclei undergo mod- 

 ifications of great consequence in the development of the future 

 spermatic elements. 



The views concerning the genetic relation of the parts of the origi- 

 nal cell to those of the resulting spermatozoon are still at variance. 

 According to Henle, La Valette St. George, and many others, the 

 nucleus of the daughter-cell gives rise to the head, while from the 

 protoplasm are differentiated the middle-piece and the tail. On the 

 other hand, Kolliker has always held, as likewise have Biondi and 

 Niessing, that the nucleus undergoes a complicated metamorphosis, 

 producing not only the head, but also the entire spermatozoon, the 

 protoplasm becoming part of the granular d6bris in which the groups 

 of developing spermatozoa lie embedded. 



