384 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



caryolymph as to the physical consistency of tlie discharged material itself, and 

 when this is formed within the nucleolus it is surrounded by the relatively firm 

 nucleolar substance and does not, therefore, assume the spherular form. In all 

 those rare cases in which Professor Chubb saw spherules within the nucleolus 

 similar to those outside they were each contained within a vacuole and were, there- 

 fore, here also surrounded by a fluid medium. 



In the great majority of cases we should expect the basophile substance result- 

 ing from the nucleolar activity to form an irregular zone on the inner side of the 

 as yet unaltered cortical region, between this and the faintly staining area, and 

 only to assume a spherular form as it is discharged into the more fluid caryolymph. 

 There is some evidence to show that this is the actual mode of accumulation of the 

 substance of the future spherules. 



The extent of the faintly staining area shows no gradual increase in size with 

 the growth of the egg, eggs of the same age and in the same pinnule possessing 

 nucleoli sometimes deeply stained and sometimes greatly destained, even in the 

 same section. On the other hand, the growth in bulk of the nucleolus does proceed 

 perfectly steadily, and shows a striking correlation with the growth of the egg. It 

 is evident, therefore, that while the faintly staining ground substance of the 

 nucleolus steadily increases in bulk, the amount of basophile substance present in 

 the nucleolus fluctuates greatly, sometimes gaining, sometimes losing, on the 

 nucleolar activity. 



Since it is only in the earlier stages of its growth that the nucleolus shows any 

 spatial relation to the chromatin, and only very exceptionally at any period shows 

 any relation to the nuclear membrane, it follows that the caryolymph must be the 

 immediate source for both these nucleolar substances. 



This source for the basophile substance is very clearly indicated by the ap- 

 pearance often seen in material in which the nucleolus readily parts with the basic 

 stain, the faintly stained nucleolus being studded all over with minute basophile 

 areas, each flush with the nucleolar surface external Ij', and projectmg irregularly 

 into the faintly stained ground substance of the nucleolus internally. This ap- 

 pearance would seem to suggest that the basophile substance enters the nucleolus 

 by diffusion through the nucleolar surface. Osmotic diffusion through the surface 

 layers of the nucleolus is also suggested bj' the mechanism of discharge already 

 described. 



The caryolymph as the immediate source for the ground substance of the 

 nucleolus is convincingly shown by the formation of the nucleolar accumulation on 

 the completion of yolk formation, for, as we have seen, this accumulation not only 

 strongly resembles the faintly staining area of the nucleolus in its staining reac- 

 tions, but its formation synchronizes with the cessation of growth on the part of 

 the nucleolus. It is impossible, therefore, to avoid the conclusion that this accumu- 

 lation represents material to which the steady increase in size of the nucleolus was 

 formerly due, and which, now that the nucleolar activity has ceased, can no longer 

 be incorporated in the body of the nucleolus. 



According to Professor Chubb the formation of the nucleolar accumulations 

 on the cessation of nucleolar activity would seem to suggest that, in so far as this 



