No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 519 
relation to those of the first generation ; and their difference 
from the latter is probably due to the fact that they have been 
produced at a time when very different physiological conditions 
exist in the nucleus. 
It is not my intention in this contribution to deal in any 
detail with those cases where double nucleoli occur in a cell, or 
those where two chemically and morphologically different kinds 
of “ nucleoli” occur in the same nucleus ; to these cases it is 
my intention to devote a special study. But preliminarily, from 
those observations which I have made on this subject, the 
following conclusions are in order. In a nucleus there some¬ 
times occurs a double nucleolus, the component parts of which 
may each represent a true nucleolus ; or such a double nucle¬ 
olus may consist of a true nucleolus apposed to a chromatin- 
nucleolus (according to my unpublished observations on the 
spermatocytes of the beetle Harpalus). Further, and this is fre¬ 
quently the case in resting spermatocytes of the first order, the 
nucleus may contain a true nucleolus separated from a chromatin- 
nucleolus ; and in Pentatoma y the account of the spermatogenesis 
of which will be shortly published by me, the unique process 
occurs of the chromatin-nucleolus being a metamorphosed 
chromosome (one of the fourteen chromosomes of the last 
spermatogonic division becoming the chromatin-nucleolus of 
the first spermatocyte) ! This peculiar structure of Pentatoma 
divides with the true chromosomes in the first reduction divi¬ 
sion. In another case where I have been able to follow all 
the developmental stages of a chromatin-nucleolus, namely, in 
cells of the hypodermis of the larva of Carpocapsa ,, I found it 
to originate from one of the granules of the nuclear reticulum, 
— a particular one of these granules (karyosomes) gradually 
increasing in size until it attains large dimensions ; during its 
growth period it is usually attached to one of the true nucleoli 
of the cell. What is of importance in these two cases (Penta¬ 
toma and Carpocapsa) is the distinction emphasized between the 
true nucleolus and a karyosome or chromatin-nucleolus : the 
latter always standing in genetic connection with the true 
chromatin, while the former, so far as my observations go, is 
never derived from this substance. These observations are not 
