112 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
“centrosome” of writers on spermatid metamorphosis. I have been 
unable to trace any connection between this body and the centrosome 
of the last maturation division since, as in previous divisions, the 
centrosome disappears during the anaphase. During the early stages. 
of the metamorphosis granules staining with hematoxylin are frequently 
seen in the cytoplasm, and in some cases may be applied to the nuclear 
membrane. ‘There may be several of these granules in a single sper- 
matid, and it is, of course, impossible to determine whether any of 
them have any connection with the centrosome. Extending out from 
the centrosome into the elongated portion of the cell is a fine fibril, 
the axial filament. At this stage the axial filament is well defined for 
a short distance from the centrosome and then gradually becomes 
thinner until it disappears altogether. ‘The spermatid continues to 
elongate (Fig. 216) while the centrosome and axial filament increase 
in size. ‘The Nebenkern becomes much elongated and travels out 
along the axial filament, part of it being continually left behind to 
form a distinct envelope about the filament. Figure 218 is a later 
stage, in which the entire Nebenkern has been converted into an 
envelope surrounding the axial filament. The nucleus lies at one end 
of the greatly elongated spermatid and is surrounded by a very thin 
layer of cytoplasm. 
From now on marked changes take place in both cytoplasm and 
nucleus. The latter becomes smaller and conical, and stains a nearly 
uniform gray with here and there minute deeply staining granules 
(Fig. 219). Figures 220-222 represent successively later stages in the 
elongation of the nucleus and centrosome. At this time, especially 
when imperfectly fixed, the nucleus usually shows a very finely fibrillar 
structure. ‘There is practically no cytoplasm surrounding the nucleus, 
although it is still plainly enclosed by the cell membrane. Figure 223 
shows the anterior end of a nearly mature spermatozoén. ‘The nu- 
cleus, which again stains deeply with hematoxylin, has become greatly 
elongated to form the head of the spermatozoon and at the anterior 
end tapers to a fine point; but there is nothing which can be consid- 
ered an acrosome. ‘The nucleus is still surrounded by the cell wall, 
but there is apparently no cytoplasm in this region and the cell wall 
is probably lost a little later. The centrosome is much elongated and 
forms the so-called middle piece, while the tail is composed of a central 
deeply staining fiber, formed from the axial filament, and an envelope 
derived from the Nebenkern, the two at this stage being indistinguish- 
able. Surrounding the central fiber and forming the greater part of 
the tail is a lighter envelope derived from the cytoplasm of the sperma- 
vite ¥ . 
