MONTGOMERY. 
[VOL. XV. 
518 
In the ova of Montagna and Rodalia they are never in contact 
with the nucleolus. In none of these three cases observed by 
me does there seem to be any genetic connection between the 
paranucleoli and the nucleoli proper. And in other cases, 
where the two are separated (this separation is the most usual 
state), no genetic connection between the two has been de¬ 
scribed ; and even in that smaller number of cases where 
they are in contact with each other at some period of their 
development, no positive proof of their genetic relation has 
been offered. Therefore we might conclude, though with re¬ 
serve, that in the greater number, if not all, cases the para¬ 
nucleoli are not derivatives of the nucleolus, but are products 
sui generis. It is the rule that the nucleolus proper appears 
in the nucleus before the paranucleoli arise, the latter usually 
arising first towards the close of the growth stages. Accord¬ 
ingly, though I cannot corroborate Hacker’s (’95) conclusions 
as to the origin of the nucleolar substance, I am inclined to 
agree with him that portions of nucleolar substance are succes¬ 
sively deposited in the nucleus, and that those portions which 
are deposited last, after the nucleus has undergone important 
physiological and chemical changes, would differ from the 
portion first produced (that of the nucleolus proper), and so 
would represent the paranucleolus. And there are certain facts 
from my own observations which would support this view. In 
the earlier stages of the maturation of the ovum of Tetrastemma 
and Zygonemertes there are a large number of nucleoli produced 
successively at the periphery of the nucleus; these then wander 
successively to the center of the nucleus, and then from that 
point again to the periphery. Now in this last stage, when the 
nuclear filaments are commencing to arise, we find, usually in 
contact with the latter, much smaller, more deeply stained 
nucleoli, and these I have termed “nucleoli of the second 
generation.” We have found, accordingly, that after the nu¬ 
cleus has passed through very marked physiological changes 
(increase in size, redistribution of chromatin), another kind of 
nucleoli appears, which may or may not be morphologically com¬ 
pared to the paranucleoli of other ova. These nucleoli of the 
second generation have neither a genetic nor a physiological 
