242 



NORMAL HISTOLOGY. 



cells, or the "cells of Sertoli," are differentiated from the others (Figs. 

 216-228). These sustentaeular cells rest with a broad base, the 



Fig. 216. 



Superficial aspect of the parietal cells of the seminiferous tube: rat. (Ebner.) /, basal 

 plates of the sustentaeular cells (cells of Sertoli), each containing a large vesicular 

 nucleus, poor in chromatin, and a distinct nucleolus of considerable size; w, spermato- 

 gonia resting upon the basal plates of the cells of Sertoli. Only a few of the spermato- 

 gonia are represented. 



Fig. 217. 



Fig. 218. 



s28 



s 29 



<<• 1 J " / w 2 f 



Sections from the testis of the rat. illustrating spermatogenesis. (Ebner.) 



Figs. 217-228.— u\ spermatogonia ; /, sustentaeular cells, or cells of Sertoli ; h, spermatocytes ; 

 s, spermatids ; sp, spermatids becoming transformed into spermatozoa : uil to wlO traces 

 the history of the spermatogonia from the resting condition to that in which they have 

 grown to become primary spermatocytes. During this process they move from the parietal 

 layer into that covering it. All, a recently formed spermatocyte; ftlS to ft20, growth of 

 the spermatocyte; A<21, beginning of the division to form secondary spermatocytes : /<22, 

 its end; 623, secondary spermatocyte, with chromatin in open spirem; A24, division of 

 the secondary spermatocyte to form two spermatids; s25, recently formed spermatid ; s26 

 to 829, growth of the spermatid. (By this time the preceding crop of spermatozoa is fully 

 developed and lias been discharged into the lumen of the seminiferous tube.) s30 and 

 s31, beginning transformation of the spermatids into spermatozoa. Their cytoplasm 

 blends with that of the sustentaeular cell. .^32 to 8p39, stages in the differentiation of 

 the spermatozoa; 10, completed spermatozoon ready to pass into the lumen of the tube. 

 ill (Fig. 227) and toll (Fig. 228) illustrate the division of the spermatogonia before they 

 begin to develop into spermatocytes. It is supposed that the sustentaeular cells aid in 

 the nourishment of the spermatids during their transformation into spermatozoa, and 

 that after the discharge of the latter the cytoplasmic process is retracted toward the base- 

 ment-membrane, bringing with it the globules of fat and cytoplasmic fragments of the 

 spermatids represented by dark spots and small round bodies in nearly all the figures. 

 This retraction is taking place at /, Fig. 219. The cells of Sertoli do not appear to mul- 

 tiply ; at least no karyokinetic figures have been observed in their nuclei. 



