602 
J. BRONTE GATENBY. 
male progerminatives, and are probably instrumental in 
checking or stimulating spermatogonial divisions. 
(3) The nutrimental conditions of the wall producing a 
male generation is hardly ever the same. 
(4) Finally, it will be seen that the spermatogonium begin- 
ning growth period may have had a very variable history. 
This is demonstrated by the variation in not only its plasma, 
but often in its nucleus. 
It can safely be said that in hardly any other group are 
the conditions under which the male cells arise so open to 
variation. 
Difference in the mitochondria of the various generations is 
principally due to the fact that a much divided line of sper- 
matogonia contains but few mitochondrial granules. When 
growth begins, in every case it seems that the mitochondria 
increase in number by dividing ; but there is some difficulty 
in observing this, though one knows this process must happen 
by the fact that spermatogonia have fewer mitochondria than 
spermatocytes, and the question is not merely a matter of 
increase of size of the granules in the growth period. Thus 
the spermatogonium, which has, so to speak, originated at the 
tail end of a large number of divisions, starts out on growth 
with fewer mitochondria. These divide, but never give rise 
to the same number . of granules as one finds in other “less 
divided” generations; but paucity in numbers is almost 
always balanced by increased size of individual granules 
(compare PI. 33, figs. 37 and 40). 
In many of the drawings in this paper mitochondria are 
shown as hollow spheres, while in others they look quite solid 
(compare PI. 32, figs. 25 and 26). The most natural explana- 
tion of this is, that for some reason the stain is more easily 
extracted out of some granules than out of others, and that 
all the mitochondria are really hollow spheres, though over- 
stains tinge the medullary zone. To test this I took a slide 
with “ solid ” mitochondria and extracted more of the stain, 
examining it at intervals. The half of the slide which was 
ever-differentiated showed most of the mitochondria as hollow 
