138 KANSAS UNIVERSITY SCIENCE BULLETIN. 



other three cells divide and develop into the primary spermato- 

 cytes. Then, assuming- that the principles of spermatogenesis 

 in the rat are the same as those Montgomery describes for man, 

 there ought to be Sertoli cells, perhaps not quite mature, for 

 each generation of germ cells in the tubule. Usually three 

 generations of germ cells — primary and secondary spermato- 

 cytes, and spermatozoa — are distinctly visible in the tubules. 

 But only when one generation of spermatozoa and Sertoli cells 

 are passing out can a second generation of Sertoli cells be dis- 

 tinguished. Where, then, are the successive quarters of ulti- 

 mate spermatogonia which contain the rod, some of which de- 

 velop into Sertoli cells before the other three quarters of ulti- 

 mate spermatogonia can divide? It would seem that they would 

 at least be visible by the time the other three quarters had be- 

 come secondary spermatocytes. 



CONCLUSIONS. 



1. The Sertoli cells of the rat do not show a rod-like struc- 

 ture, but those of the cat do. 



2. There is no definite connection between Sertoli cells and 

 germ cells until the spermatozoa are beginning to form. 



3. The number of spermatozoa to each Sertoli cell varies 

 from 6 to 12 in the rat. 



BIBLIOGRAPHY. 



Debaisieux, P. 



1909. Les debuts de l'ovogense dans le Dytiscus marginalis. La 



Cellule 25. 



Flemming, von W. 



1897. Ueber die Chromosomenzahl beim Menschen. Anat. Anz. 

 Bd. 14. 



Guyer. M. F. 



1910. Accessory chromosomes in man. 



Biol. Bull. vol. 19. 

 1900. Spermatogenesis of Normal and Hybrid Pigeons. 



Jordan, H. E. 



1912. Heterochromosomes in mammals. 



Proceedings of Soc. for Experimental Biol, and Med. vol 

 10, No. 1. 



Montgomery, Thomas H. 



1911. Differentiation of the Human cells of Sertoli. 



Biol. Bull. vol. 21. 



Morris, J. T. 



1909. A note on Orange G. counterstaining suggesting a useful method 

 in the management of embryonic tissues. Anat. Rec. vol. 3. 



