521 
gonial mitosis and synizesis. In no event can synizesis (and synapsis ) 
be regarded as the result of a passivity on the part of the nuclear 
chromatic network; on the contrary, all the evidence indicates specific 
activity of this structure. 
A significant phenomenon appears in the early prophase of the 
first maturation mitosis: the chromosomes resulting from the segmen- 
tation of the double, mossy, only slightly chromatic spireme begin to 
grow compact and deeply chromatic first at that end next, and at- 
tached to, the nuclear wall (fig. 19). This would seem to indicate 
that the raw material for chromatin production has a direct extra- 
nuclear (cytoplasmic) origin. 
It remains to note briefly the presence of mitochondria. It is 
unfortunate that a material so favorable from the standpoint of 
number and size, should yet be so unfavorable from that of origin 
and fate. Nothing definite may be said regarding source or function 
of mitochondria in the bat. No evidence appears for the direct origin 
of mitochondria from the nucleus such as I have described for the 
opossum. Mitochondria are already abundantly present as small 
spherical and bacillary elements in dividing spermatogonia (figs. 1 to 3). 
The fact that they do not appear, or at least only very sparsely, in 
resting spermatogonia indicates — beside some direct evidence — that 
they have origin as cast-off fragments of chromosomes at mitosis. 
Mitochondria are present at all subsequent stages. While the sperma- 
tozoa have a distinct spiral filament in connection with the middle 
piece, no direct demonstration appears that mitochondria contribute 
to its formation. However, in conformity with what is known to oc- 
cur in many other forms such fate of the mitochondria in the formation 
of the spiral filament of the bat is reasonably presumable. 
The interstitial cells also are locaded with mitochondria (fig. 24). 
Here the prevailing form is oval or bacillary. The fact that the mito- 
chondria appear very clearly and abundantly in this tissue (FLEMMING 
fixed), shows that they react to osmic acid in the manner of fat, and 
are distinctly of a lipoid nature. 
Summary and Conclusions. 
1) Synizesis in the bat is the result of an active polarization pro- 
cess of the nuclear reticulum. It cannot be regarded as due to a 
passive retention of an original condition on the part of the reticulum 
while the karyolymph is greatly augmenting; nor as the result of a 
mechanical effect of such increase of nuclear matrix. The idiozome 
probably plays an accessory röle in the production of synizesis. 
