162 
Spermatogenesis in Ixodes 
from the surrounding plasma by their clearer contents and increasing greatly 
in size (PL XI, figs. 11, 13, 14). Among these vesicles one especially, 
situated opposite the internal end of the nucleus, attains a considerable size 
(Fig. 15). Finally the vesicles run together and occupy the whole mass of 
the ectoplasma; they are, as this shows, also plasma structures and not 
liquid inclusions. 
The part played by the centrosome during this evolution of nucleus and 
plasma is not yet described. When last seen, it was at the telophase of the 
second maturation division, half hidden among the chromosomes at the part 
of the cell opposite the spindle. The most difficult part of the whole investiga¬ 
tion was the subsequent following of the centrosome. The very important 
part it plays everywhere in the development of the spermatozoon makes an 
accurate observation of it through the several phases of the cell-metamorphosis 
indispensable. One meets indeed not infrequently with investigations on 
spermatogenesis wherein the centrosome has been invisible at some stage, 
and in which its behaviour is only traceable by inference. Such is also 
unfortunately the case with our subject. In the meta- and ana-phases of the 
mitoses the centrosomes are easy to observe as triangular points, surrounded 
by a strong radiation, but, already at the telophase, the centrosome, as has 
been explained, is not always easy to find. And in the young spermatids it is 
generally very difficult to distinguish the centrosome from the similarly 
granular mitochondria: none of the special staining methods recommended 
in the literature for this purpose was of any use here, although many have 
been tried; the mitochondria cannot be decolourized in such a way that the 
centrosome remains, nor is this element, as is very often the case in other 
objects, surrounded by any characteristic plasmatic structure such as radiation 
or clear plasma zone, which could be used as a means of identification. On 
close examination it is indeed possible to fix the position of the centrosome 
at least approximately. Here the telophase must be the starting point. In 
it the centrosome lies, as has been already mentioned, close to the chromosomes 
and always at the pole of the nucleus opposite to the mitotic spindle. At this 
pole there is, even after the reconstruction of the spermatid nucleus, in favour¬ 
able preparations, a minute deeply coloured structure, which must undoubtedly 
be identified with the centrosome (Fig. 3). As the nucleus begins to approach 
the spindle side of the cell surface, and later on becomes rod-shaped, it is to 
be expected, that the centrosome would even still be found at the internal 
end of the nucleus. As a matter of fact, at this place, in many preparations, 
can be seen a very small, deeply staining granule (Fig. 7), which may be 
regarded as the centrosome. In the following stages the centrosome unites 
even more closely with the internal end of the rod-like nucleus (Figs. 10-12, 14). 
It appears in close union with the end of the nucleus, surrounded by a clear zone, 
and opposite the previously mentioned conical projection of the endoplasma. 
In the following development the nucleus, the centrosome and the mito¬ 
chondria of the endoplasma play the most considerable part and consequently 
