520 
the interpretation that it represents simply the result of a very rapid 
growth of the cell body and nuclear matrix relative to the chromatin: 
1) In the period directly preceding synizesis, the nuclear reticulum 
is delicate and wide meshed and coextensive with the nucleus (figs. 4 
to 6). During synizesis it increases in amount and becomes coarser 
and more chromatic and is segregated at the idiozome pole (figs. 7 
to 11). The nucleus itself has meanwhile enlarged very little if at 
all (compare figs. 4 and 7; and 6 and 13); moreover, the amount of 
chromatin seems clearly to have been increased, at any rate relatively 
much more than the nuclear matrix. Hence the nuclear reticulum 
must have moved and become rearranged. Since it is invariably 
located at the idiozome pole, the centrosphere would seem to be an 
active accessory factor in determining the physical phenomenon of 
synizesis. 
2) Following synizesis the nucleus enlarges considerably (figs. 13 
to 19). Coincident with this increase occurs a disentanglement and 
definite rearrangement of the apparently promiscuously compacted 
threads of the synizesis mass, and a scattering of its components (bi- 
valent chromosomes) throughout the nucleus. Since the reticulum can 
actively dispose itself after synizesis, intrinsic properties plus the 
attractive influence of the idiozome may very well suffice also to effect 
synizesis. 
3) Finally, conditions are exactly the reverse of those requisite 
to produce synizesis by growth of the nuclear matrix while the 
chromatic network passively remains unchanged at one pole: when the 
nucleus increases greatly in size (i. e., during postsynizesis) the 
synizesis mass opens up and disperses its elements; while the synize- 
sis mass was forming, the nucleus remained practically unchanged in 
bulk and at the same time that the chromatic network itself increased 
in amount. 
Synizesis and synapsis are accordingly, in the bat, the morpho- 
logical expression of active changes in the chromatic network itself, 
not the result of a passivity while the nuclear matrix and cell body 
changed (grew) about it. 
An interpretation of synizesis that suggested itself, and which 
may accord with the facts in some instances, namely; that it re- 
presents the still compact anaphase chromosome mass of the last 
(spermatogonial) mitosis — which interpretation likewise would account 
for its location at the idiozome pole — is clearly untenable in the 
case of the bat, since there is no doubt of the interpolation of a 
definite resting phase as above described between the last spermato- 
