SPERMATOGENESIS. 



375 



process, with the exception that here the different stages are seen 

 side by side in the seminiferous tubule and without any apparent 

 sequence, making the successive stages more difficult to demon- 

 strate. The various generations of cells form columns, and are 

 arranged in such a manner that the younger are found near the 

 lumen and the older close to the wall of the tubule. (Figs. 301 and 



9 



Fig. 301. Schematic diagram of section through convoluted seminiferous tubule 

 of mammal, showing the development of the spermatosomes. The number of chromo- 

 somes is not shown in the various generations of the spermatogenic cells. The pro- 

 gressive development of the spermatogenic elements is illustrated in the eight sectors 

 of the circle : a, Young sustentacular cell ; b, spermatogonium ; c, spermatocyte ; d, 

 spermatid. In I, 2, 3, and 4 the spermatids rest on the enlarged sustentacular cell in the 

 center of the sector ; on both sides of the sustentacular cells are the spermatogenic or 

 mother cells in mitosis. In the sectors 5, 6, 7, and 8 spermatozoa are seen in ad- 

 vanced stages resting on the sustentacular cells, with new generations of spermatids on 

 each side. [From Rauber (after Brown) with changes (after Hermann).] 



302.) These columns are separated from each other by high sus- 

 tentacular cells, or Sertoli's cells or columns. The metamorphosis 

 of the cells into spermatids and spermatosomes is accomplished 

 by the changing of the cells bordering upon the lumen and then 

 of those in the deeper layers, etc., into spermatids and then 

 into spermatosomes. During this process the spermatids arrange 



