The second extra-nuclear body I shall call the acrosome, as it
forms the point of the spermatozoon head. I could not trace its
origin, because the fixation was not definite in some of the early
stages. Fig. 4 shows a small, darkly staining body, which may be a
centrosome, but more likely is the beginning of the acrosome, of
which figs. 7, 9 and 10 show developing stages, and figs. 11, 13 and
15 more advanced ones. Sometimes the central portion stains darkest
(figs. 11, 32, and 36), but more frequently there is a small clearer
space in the center surrounded by a ring or band of darker material.
(Figs. 10, 13, 27, and 30.) This ring usually stains darker on one
side, very often on the side toward the nucleus.
The position, which is, with few exceptions, in the angle between the
nucleus and the nebenkern, induces me to consider the differently
staining bodies as the same organ of the cell. For some time after
the nebenkern has disappeared the acrosome keeps its position;
then it approaches the nuclear wall, flattens against it, and
later wanders to the apical end, where it forms the tip of the
spermatozoon. (See figs. 32-36 and 39-42.) Fig. 16 shows the acrosome
back of the nebenkern. It is not an isolated example, still, I think,
it is an abnormality. Fig. 37 shows an apparent division of the
acrosome. I did not see enough instances to consider it a regular
occurrence.