536 MONTGOMERY. [Vol. XV. 



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 Alontagita 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 diiificult 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 Chironovms 

 (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 



