THE REPRODUCTIVE SYSTEM 



341 



layers: (a) An outer layer composed of several rows ol llaUened con- 

 nective-tissue cells which closely invest the tubule; (b) a thin base- 

 ment membrane; and (c) a lining epithelium. The epithelium con- 

 sists of two kinds of cells, the so-called supporting or susientacular 

 cells and the gandular cells proper, the s per mato genie cells. 



The suskntaciilar cells, or columns of Sertoli, are irregular, high, 

 epithehal structures, whose bases rest upon the basement membrane, 



sf 5 



Fig. 235.— Cross Section of Convoluted Portion of Human Seminiferous Tubule 

 X480. (Kolliker.) M, Basement membrane; i, its inner homogeneous layer; fs, its 

 outer fibrous layer; s, nucleus of Sertoli cell; sp, spermatogone; sc, spermatocyte; sc' , 

 spermatocyte showing mitosis; sf, nearly mature spermatozoon; sf , spermatozoon free 

 in lumen of tubule; d, degenerating nucleus in lumen; /, fat droplets stained by osmic 

 acid. 



and wliich extend through or nearly through the entire epithelium 

 (Fig. 236,5). Their sides show marked irregularities and depressions, 

 due to the pressure of surrounding spermatogenic cells. Their nuclei 

 are clear, being poor in chromatin and their protoplasm contains 

 brownish fat droplets. The cells of Sertoli have long been considered 

 as sustentacular in character. It has recently been suggested that 

 these cells are derived from the spermatogenic cells, but that, in- 

 stead of developing into spermatozoa, they undergo retrograde changes, 



r 



