MONTGOMERY. 
[Vol. XV. 
536 
It would be premature to attempt to decide the exact manner 
in which the nucleolar substance is concerned in the metabolism 
of the cell. But the facts at least show that it has an extranu- 
clear origin, and is especially abundant in growing nuclei, which 
shows that it stands in intimate connection with the phenomena 
of nutrition of the nucleus. 
Vacuoles are characteristic for certain stages in the develop¬ 
ment of many nucleoli, especially those of germinal vesicles. 
For the nucleoli of the ova of Montagna and Doto , I showed 
that the vacuolar substance is at first present in the form of 
small globules in the nuclear sap, that these become applied 
against the surface of the nucleolus, and, finally penetrating into 
the latter, represent within it the vacuoles. I was unable to 
decide the mode of derivation of the vacuoles for the other 
nucleoli studied. So in some cases this vacuolar substance 
would appear not to be a derivative of the ground substance of 
the nucleolus, but to be derived from without the latter. Thus 
such nucleoli may be considered as diosmosing structures. The 
manner of growth of nucleoli is apparently by a process of 
apposition of smaller particles of nucleolar substance to their 
surfaces, and the addition of vacuolar substance to them differs 
from this only in that the vacuolar substance is intussuscepted. 
This vacuolar substance may be also a product of the nutritive 
processes of the nucleus. 
It is a difficult question to determine whether the nucleolus 
at some stage of its development should not be considered a 
nuclear organ. In most nuclei it has a regular shape, in 
others it may be oval; in many cases the nucleolus has no 
regular shape, and in the salivary gland cells of Chironomus 
(according to Balbiani) it is convoluted. From the facts at 
hand we may conclude that the shape of the nucleolus is 
pretty constant for the particular species of cell. Now, tak¬ 
ing constancy in form as a criterion of an organ, one might 
conclude that the nucleoli are organs. But, on the other hand, 
the most frequent form of the nucleolus, namely, the spherical, 
might simply be due to its thin fluid consistency, and when it 
is more viscid in consistency its shape would be more irregular. 
Thus Rhumbler (’93) concludes that the irregular nucleoli of 
