1944 



HUMAN ANATOMY. 



membrana propria, and the youngest, from which the spermatic filaments are directly- 

 derived, next the lumen of the tubule. The first generation, the spermatogones, lie 

 at the periphery between the cells of Sertoli, and, although small round elements, 



Seminiferous tubule,. 

 cut obliquely 







Blood-vessel 



I 



\M Vio 



Tunica albuginea — u,^ iL <> 



h\ ^ 



Seminiferous tubule X 

 cut transversely f ii 'M 



Group of interstitial cells 



-4 — 44w- 



Tunica vaginalis 





Portion of cross-section of testis, showing dense fibrous envelope 

 and adjacent seminiferous tubules. X 3°- 





^:m 



possess nuclei exceedingly rich in chromatin. The division of these cells results in 

 two cells, of which one retains the position of the parent cell, which it replaces as a 

 new spermatogone destined for a succeeding division, while the other passes inward, 

 enlarges, and becomes a mother cell or primary spermatocyte of the second genera- 

 tion. This element, conspicuous by reason of its size and large nucleus, undergoes 

 mitotic division and gives rise to daughter cells or secondary spermatocytes. The 

 latter almost immediately divide and produce smaller cells, the spermatids, by the 

 transformation of which the spermatic filaments are directly produced. It is impor- 

 tant to note that the spermatids 

 Fig. 1654. contain only one-half of the num- 



ber of chromosomes normal for 

 the ordinary (somatic) cells, a 

 like reduction (page i8) occur- 

 ring in the matured ovum. 



Spermatogenesis. — The 

 cytological cycle resulting in the 

 production of the spermatozoa 

 from the epithelial cells lining the 

 seminiferous tubules comprises 

 four principal stages : ( i ) divi- 

 sion of the spermatogones into 

 spermatocytes ; (2) division of 

 the latter into spermatids ; (3) 

 transformation of spermatids into 

 spermatozoa ; (4) completed dif- 

 ferentiation and liberation of sper- 

 matozoa. The changes incident 

 to the first and second of these 

 stages have been outlined ; a brief account of the subsequent changes may here be 

 added. The spermatids, at first small cells with round nuclei, elongate, their nuclei 

 coincidently becoming oval and smaller, but rich in chromatin, and shifting to the 



V fe'm'Ofe-, :v / jyii-j^*^ Epithelial 



tubule 



mm-mt 



"^ 



W^J^^ 



^^S-sS 



=^^V' 





Interstitial 

 cells 



-i VJ" 







'■Intertubular 

 connective 

 tissue 



-Tunica 

 propria 

 of tubule 



Group of interstitial cells lying wfthin intertubular stroma. X 300. 



