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MONTGOMERY. 
[Vol. XV. 
posited evenly throughout the nucleus, and not only at the 
periphery. And his deductions are based in great part, as those 
of most other investigators, on the study of maturation mitoses, 
and he had not observed their first mode of origin, namely, their 
origin in nuclei which are not in the prophases of mitosis, but 
are only gradually becoming differentiated from somatic cells. 
I have found no evidences in any cell that the nucleoli stand 
in any genetic relation to the chromatin elements of the 
nucleus ; and while the chromatin may derive substances from 
the nucleoli, I am unacquainted with any observations which 
show that the nucleoli derive any part of their substance from 
the chromatin. In all the cases observed by me, the nu¬ 
cleus appears to assimilate a substance or substances from the 
cytoplasm, and after this substance has entered the nucleus it 
apparently undergoes there a chemical change, and becomes 
deposited on the inner surface of the nuclear membrane in the 
form of masses of varying dimensions, which may be either 
globular or irregular in shape, according as they are fluid or 
viscid in consistency. In the case of the ova of the nemerteans 
the substance taken up into the nucleus, and which there 
becomes deposited in the form of nucleoli, is sometimes exactly 
similar to the substance of the yolk-balls which lie in the cyto¬ 
plasm; in other cases it is probably similar to those metabolically 
changed portions or inclusions of the cytoplasm, out of which 
the yolk-balls are later differentiated. In Linens , indeed, the 
yolk-balls may often be found halfway through the nuclear mem¬ 
brane, and their appearance is exactly similar to that of the 
nucleoli. In the mesenchym cells of Cerebratulus the substance 
of the nucleoli appears to be identical with that of the numer¬ 
ous nutritive granules which are dispersed in the cytoplasm ; 
the latter globules arise in the cytoplasm before the nucleolus 
appears in the nucleus, and as soon as they become numerous 
in the neighborhood of the nucleus, peripheral nucleoli begin to 
appear in the latter. In the subcutical gland cells of Piscicola 
the nucleolus, at the time of its most rapid growth, is apposed 
to the nuclear membrane; but when this period of volume- 
increase has ceased, it is never found in this position. Further, 
the paranucleoli of Rodalia appear first in contact with the 
