ON SPERMATOGENESIS IN THE RAT. 
363 
velopment the heads of the spermatozoa travel downwards 
towards the base of the cell, so that they reach the outer layer ; 
on the completion of the process they travel back again, and 
finally are thrown off into the lumen. The “ round cells,” 
which occupy the spaces between the columns of spermatozoa, 
according to von Ebner, serve only for the production of the 
liquid portion of the semen. 
It is obvious that this account is due to an erroneous inter- 
pretation of the appearance of columns of spermatozoa, which 
is so conspicuous a feature in the testis of the rat ; there 
cannot be the least doubt that it is from the “ round cells ” 
that the spermatozoa are derived, and that they are not 
produced endogenously in the protoplasm of the supporting 
cells. 
Merkel, in 1871, gives a very different account of the 
process to that of von Ebner. He considers that the sperma- 
tozoa are derived from the small round cells which, according 
to von Ebnor, undergo liquefaction ; these become embedded 
in cavities which are hollowed out in the protoplasm of the 
supporting cells, thus producing the spermatoblasts of von 
Ebner, and in these supporting cells undergo development into 
spermatozoa. 
Sertoli, in 1874, gives a much fuller account of the process. 
He describes fixed, or supporting, and mobile cells, which he 
divides into three classes. 1. “ Germinative ” cells, which 
are small, and situated in the outer layer between the bases of 
the supporting cells. 2. “Seminiferous” cells, which are 
larger, and form the second layer, and correspond to the 
germinative cells of the preceding generation, which have 
increased in size, and become pushed inwards by the formation 
of a new layer of germinative cells, between them and the wall 
of the tubule. 3. “ Nematoblasts,” which are small cells 
produced by the division of the preceding generation of 
seminiferous cells, and destined to develop into spermatozoa. 
Sertoli gives no account of the mode of production of the ger- 
minative cells. 
Lavalette St. George, who has published numerous papers 
