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 oocyte) 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 oocytes, 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 



