84 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
linin is considerably increased, and the fine radiating fibrils which 
extend out through the nucleus become more abundant. 
During stage f the plasmosomes, of which there are usually two or 
three, reach their greatest size, and in the latter part of this, or in the 
following stage become more or less irregular in shape and often break 
up into a number of irregular fragments. At the same time they tend 
to stain with iron hematoxylin, so that they often resemble masses of 
chromatin. 
I have often noticed a rounded body in the cytoplasm which strikingly 
resembles a plasmosome. ‘This body is more common during stage 
f, although I have occasionally found it at a considerably earlier period. 
It is often closely applied to the nuclear membrane, but whether it is 
a plasmosome which has been extruded from the nucleus, I have been 
unable to determine. Certainly, some of the plasmosomes are never 
cast out into the cytoplasm, but degenerate within the nucleus at a 
little later stage. 
2. Monosome. 
Having described the changes in the autosomes during the growth 
period, I will now take up the history of the monosome during the 
same period. During the telophase of the last spermatogonial divi- 
sion (Plate 2, Figs. 22, 23) the monosome retains its compact structure 
and remains enclosed in a separate vesicle. At this stage a deep 
furrow or groove can often be distinguished extending along one side 
of the nucleus, and in such cases the monosome usually lies along the 
opening of the groove. This is especially well shown in cases where, 
on account of imperfect fixation, the chromatin is shrunken away 
from the nuclear membrane (Figs. 24, 25). Very often the mono- 
some is more or less completely divided by a transverse constriction 
into two unequal parts. 
During the succeeding resting stage (a) of the primary spermato- 
cyte the monosome still remains enclosed in a separate vesicle, and, 
as in the preceding stages, is an elongated homogeneous deeply stain- 
ing element often showing a more or less distinct bipartite structure 
(Fig. 23). In stage b (Fig. 28, Plate 7, Figs. 99, 100) there is little 
change in the appearance of the monosome, but in the next stage 
(c) it no longer lies in a distinct vesicle, but comes to lie within the 
common nuclear membrane (Fig. 29). During this stage there is 
little change in the monosome except that it becomes somewhat flat- 
tened and irregular in shape. 
In stage d the monosome (Plate 2, Figs. 31, 32; Plate 7, Figs. 101, 
Ta. 
