THE MALE REPRODUCTIVE ORGANS. 



209 



FIG. 251. 



exists ; inside the latter lies the lining of epithelial cells. The pre- 

 cise character of the cells within the tubule depends upon the 

 condition of functional 

 activity of the organ ; the 

 notable differences distin- 

 guishing the elements with- 

 in the resting gland from 

 those found in the active 

 organ depend largely upon 

 the infrequency within the 

 former, and the almost uni- 

 versal presence within the 

 latter, of cells actively en- 

 gaged in karyomitotic divis- 

 ion. The different tubules, 

 however, exhibit great vari- 

 ation in the exact stage 

 of these changes, adjacent 

 canals, and, in fact, parts of 



the Same One Often present- Transverse section of seminiferous tubule from human 



testicle : a, membrana propria ; b, zone of parietal cell? 



ing the extremes OI the c> mother-cells undergoing division ; d, daughter-cells, Oi 

 Cycle side bv Side spermatoblasts ; e, partially-developed spermatozoa ; f t 



, surrounding intertubular connective tissue. 



Next the basement- 

 membrane of the seminiferous tubule lies a layer of low cuboidal 

 nucleated parietal cells ; this peripheral zone contains cells of 

 two kinds: (i) the sustentacular cells, or Sertoli's columns, 

 which take no part in the formation 

 of the generative elements, and (2) 

 the spermatogenic cells, which pro- 

 duce elements intimately related to the 

 development of the seminal filaments. 

 Inside the outer, peripheral layer, in 

 functionally active organs, an irregular 

 second zone contains many elements with 

 large transparent nuclei and chromatin 

 figures, indicating the progress of cell- 

 division ; these are the mother-cells, Section of testicle of do B , including 



. . ... part of seminiferous tubule : a, zone of 



the derivatives Of the SpermatOgeniC Cells parietal cells containing sustentacular 



of the outer zone, and, in turn, the parents <* ements (/)= *. mother -ceils; c , 

 of a numerous progeny of smaller daugh- 

 ter-cells. The latter constitute the 

 spermatids, from the metamorphosis 



of which the spermatozoa are later directly derived. The inner 

 zone of the tubule is frequently occupied by fan-shaped groups of 



14 



FIG. 252. 



daughter-cells ; d, free nuclei of sper- 

 matoblasts and developing sperma- 

 tozoa. 



