3/8 THOMAS H. MONTGOMERY. 



the distinction of Scrtoli cells and germ cells: it becomes trans- 

 mitted without division to one quarter of tin- ultimate spermato- 

 gonia, and that quarter transforms into Sertoli cells. Under 

 these conditions, on account of the precision of the process, this 

 rod must be regarded as a Sertoli determinant, and as a cyl<>- 

 plasmic and not a nuclear determinant. Whether the rod, or its 

 substance, emanated fn the first place from the nucleus, can be 

 determined only by some fortunate observer who has more and 

 better fixed material than was in my hands. But there is no 

 reason to regard it as mitochondrial, as a chondriosome, because 

 granular mitochondria have been described in mammalian Sertoli 

 cells by Benda and others; in my material no mitochondria were 

 seen in the spermatocytes and spermatids, they were evidently 

 dissolved by the action of the fluid of Zenker, and it is therefore 

 probable they were dissolved also out of the spermatogonia. 



The rod that comes to determine the Sertoli cells increases in 

 size while in the cytoplasm, becoming most voluminous in the 

 ultimate spermatogonia; outside of the nucleus, also, occurs its 

 process of abstriction of the primary rodlet and the division of 

 the latter into the secondary rodlets. It is therefore clearly an 

 extranuclear determinant of the Sertoli cell; and this as yet 

 unique process of somatic differentiation seems to be controlled 

 by an extranuclear body. 



It has not been my intention to decide upon the function of the 

 Sertoli cells. They increase greatly in size to produce a syncytial 

 mass loaded with intracellular droplets, probably of fatty nature; 

 they envelope closely the rapidly growing spermatocytes and 

 for this reason they are generally supposed, and probably cor- 

 rectly so, to nourish this generation of germ cells. The fluid 

 within the seminiferous tubules contains, so far as I have ob- 

 served, neither erythrocytes nor leucocytes, therefore is probably 

 derived from the droplets of the Sertoli cells and not from the 

 blood scrum. The spermatids at the commencement of their 

 histogcnesis lose their first connection with the Sertoli cells, while 

 the nearly mature spermatozoa exhibit their heads buried in tin- 

 substance of the Sertoli cells; the latter is then a second orient. i- 

 linii of the germ cells to the Sertoli cells, one that cannot subserve 

 nutrition, for the developing spermatozoa do not inrre.i-e in 

 size, but which is rather, as Loisel ('07) has shown, the r\piv ion 



