62 Papers from the Marine Biological Laboratory at Tortugas. 
nutritive material from the nucleolus. That only a small portion of the 
chromatin material of the nucleolus is contributed to the growth of the 
chromosomes is very clear, but whether the extra portion of matter is similar 
in chemical nature to that which goes into the chromosomes, and whether this 
material changes its chemical nature on entering the chromosomes, I am 
unable to determine, staining reaction giving no indication of such a change. 
It is possible that some of the chromatin-like material stored in the nucleolus 
is waste material and the product of metabolic process of the growing egg. 
The fact that this residue, as well as the plastin ground-substance, are both 
ultimately resorbed by the cytoplasm gives some color to this latter view. 
However, it seems more probable that all the material (chromatin as well as 
plastin) is of closely similar chemical composition and has similar nutri- 
tive value, whether it passes into the chromosomes or cytoplasm of the mature 
egg. It seems more reasonable that excretion products consequent upon cell 
metabolism should be voided continually, instead of being stored in the same 
structure in common with the undoubted nutritive material. Moreover, I 
have no evidence to show any direct genetic relation between the material 
of the disappearing nucleolus and the achromatic structure of the egg. 
The nature of my material has made it impossible for me to trace the 
origin of the nucleolus from its earliest stages, but the fact that for a 
time it appears to grow by additions of material from without the nucleus 
(as indicated by the varying staining reaction of the cytoplasm during the 
growth-period of the odcyte) adds support to Montgomery’s view that the 
nucleoli of all cells are of extranuclear origin. The nucleolus increases in 
size still more by the addition of the chromatin surrendered by the post- 
synaptic spireme as it segments and condenses into chromosomes. What the 
chemical alterations which accompany this local change and morphological 
transformation of the chromatin are it is idle to conjecture. 
If my interpretation of the vacuoles which are seen in the nucleoli of the 
living egg is correct, the chromatin at first enters the nucleolus in the shape 
of spherules or fluid drops of chromatin. This fluid chromatin is contin- 
ually imbibed by the plastin ground-substance, which increases in amount 
as the chromatin content increases, being probably manufactured by the 
chromatin and, as also the linin, representing probably merely a different 
phase of the same substance. During this local change the chromatin seems 
to alter its physical composition from a fluid to a more or less viscid constitu- 
ency. The vacuoles that appear in the sectioned odcytes, and which take a 
stain similar to that of the underlying plastin, thus represent the remains 
of the spherules of fluid chromatin after this has been incorporated into the 
main mass of the nucleolus. Fusion of several such spherules will leave 
large vacuoles in the nucleolus. When all of the spherules are entirely filled 
with chromatin, sections of such nucleoli stained with specific chromatin 
stains (such as iron hematoxylin) appear homogeneous. Stains for which 
