358 
HERBERT H. BROWN. 
broken off short. This, however, is readily explained, when it 
is considered that the tubules were broken up with needles, by 
which process the inner part of the supporting cell contain- 
ing the young spermatozoa becomes broken off from the base 
which contains the nucleus, and is found to remain adherent 
to the basement membrane. 
The manner in which the oval nucleus becomes transformed 
into the head of the spermatozoon will be understood from fig. 
22. The nucleus increases in length and projects more and 
more from the cell, and the thickened part of the nuclear 
membrane progresses so as to cover the whole of the pro- 
jecting portion. Soon the nucleus begins to curve, the curva- 
ture first appearing near the apex, presumably owing to an 
increased growth of one side of the thickened membrane. As 
development goes on the curvature increases, and the denser 
portion involves more and more of the substance of the 
nucleus. 
The thickening of the nuclear membrane is apparently 
due to a condensation of the nuclear substance and its trans- 
formation into that of the head of the spermatozoon, which, 
beginning at the surface and at the outer pole of the nucleus, 
progresses until the whole nucleus is converted into the 
spermatozoon head. 
During this time the cilium which springs from the inner 
extremity of the cell has reached a considerable length, but 
very little progress has been made with the development of 
the middle piece of the spermatozoon, although the cell 
protoplasm has elongated to some extent. 
The young spermatozoon is now (fig. 22, l ) pyriform in 
shape, the base of the hooklike nucleus being inserted into the 
narrow end of the cell, a long cilium springs from the broad 
end, and connecting the nucleus to the cilium is a delicate 
filament which can only be seen with some difficulty ( vide figs. 
17 and 6, c'). The remainder of the process is occupied chiefly 
by the development of the middle piece of the spermatozoon 
(figs. 18 — 20). The cell protoplasm rapidly elongates and 
assumes a club-shaped form, since the upper extremity which 
