804 
Proceedings of the Royal Society 
clear refracting nuclei, from both of which sperms were developed : 
he emphasised the cellular homology of the spermatozoon, deriving 
the head from the nucleus, and the tail from part of the protoplasm, 
while Kolliker was more inclined to regard the whole as a modified 
nucleus. 
That the simple developmental history described by Kolliker and 
Henle did not express all the facts of the case was proved by the 
researches of Sertoli, who (1865) described in the seminal tubules 
certain “ ramified cells” which projected between the round cells, 
and were often branched internally, while the peripheral end of 
each, with the nucleus, was in direct contact with the wall of the 
canal. He regarded their function, however, as only secretory, and 
contrasted them as epithelial and fixed, with the round, mobile cells 
which had the direct role of producing sperms. This discovery 
was abundantly confirmed, but especially by Merkel, who described 
(1871) large cells lying close to the tunica propria , which he called 
Stutzzellen , and regarded as forming a supporting framework for 
the adjacent round cells from which the spermatozoa developed. 
These round cells had been hitherto regarded as alone directly 
essential to spermatogenesis, but a contrary opinion was maintained 
in the classic research of Yon Ebner (1871). Within the endo- 
thelial tunic of the seminal canals of the rat, he described a layer 
of two kinds of cells — (a) round granular cells, and (b) larger, 
elliptical cells, the latter confluent at the base, and forming a proto- 
plasmic layer or Keimnetz . The inner end of each of these large 
cells enlarges and divides, forming irregular digitate prolongations 
which project into the lumen of the duct. At the base of the 
whole cell, which with its prolongations he termed a Spermatoblast , 
the primitive nucleus remains undivided, while at the base of each 
lobe a nucleus is observed, which he ascribed to endogenous 
origin. The nucleus of each digitation elongates to form the main 
portion of the head of a spermatozoon, and a thin film of protoplasm 
elongates into the tail. The heads of the resulting spermatozoa at 
first press downwards within the spermatoblast, reaching almost to 
the Keimnetz ; their tails protrude into the lumen. When finally 
liberated the sperms curl themselves up to roll down the seminal 
tubule, and the more or less branched stump of the spermatoblast 
is left bare. The round cells take no part in the process (though 
