ON SPERMATOGENESIS IN THE RAT. 
365 
mammals. He describes the development of spermatozoa 
from small cells resulting from the division of the inner seminal 
cells ; these daughter-cells are at first free in the tubule, but 
gradually form fan-shaped groups, which sink between the 
inner seminal cell towards the wall of the tubule. 
Klein has not observed the existence of supporting cells, to 
which the groups of spermatozoa are attached, and offers no 
explanation of this grouping. 
Schafer, in the ninth edition of Quain’s f Anatomy, 5 in 1882, 
gives a short account of the testis of the Rat ; he attributes 
to the small cells of the third layer a nutritive function, and 
considers that some of the proliferating cells (the large cells of 
the second layer) give rise by their division to groups of sper- 
matozoa, while others form the small cells, which ultimately 
break down and liquefy. 
Renson, in the ‘ Archives de Biologie, 5 1882, gives a descrip- 
tion of mammalian spermatogenesis, taken chiefly from a study 
of the process in the Rat, which agrees very closely in most 
points with the result of my own investigations. 
Renson traces the origin of the spermatozoa to the small 
round cells of the outer layer, which he calls after Sertoli, 
“ germinative 55 cells, and which make their appearance sud- 
denly in the outer layer upon the basement membrane, but 
he has not been able to discover in what manner this new 
layer of cells is produced, and the production of spermatozoa 
perpetuated. 
The germinative cells increase in size, and become in the 
next cycle the “ seminiferous 55 cells which form the second 
layer. The seminiferous cells divide by karyokynesis into 
groups of daughter cells, which he calls “ cysts.” The “ cysts 55 
disintegrate, and their component cells, the “ nematoblasts, 55 are 
set free. Soon they contract a connection with the supporting 
cells, in which they become embedded in groups. Finally, 
when this development is completed, they are thrown off by 
the supporting cells into the interior of the tubule. Renson 
also describes the appearances presented by the nematoblasts 
during their development, as studied by teased preparations 
