432 KING. [VoL. XIX. 
granular yolk-nuclei are undoubtedly composed of nutritive 
material which is subsequently aggregated into yolk spherules. 
In some instances the substance of the vitelline bodies seems to 
be transformed directly into yolk spherules; the intermediate 
stage, that of the formation of yolk-nuclei, being omitted. 
This would seem to indicate that the vitelline bodies are them- 
selves but aggregations of nutritive material which is in a 
semi-fluid condition rather than in the form of granules. It 
may be that during the early stages in the development of the 
ova “yolk is present in the cytoplasm in the form of a diffused 
unstainable fluid,’ as Montgomery has suggested, and that 
this fluid is first collected into the rounded vitelline bodies and 
jater changed into yolk spherules. 
The part taken by the nucleus in the formation of yolk in 
the egg of Bufo is as yet obscured. I have never seen any 
nucleoli or any minute granules leave the nucleus which might 
have an influence on the formation of the yolk. If, as seems 
probable, the nucleus directs and controls the nutritive pro- 
cesses in the cell, then in the formation of yolk it must act 
either through a fluid substance which it gives out into the 
cell-body, or it must exert its influence directly on the deuto- 
plasmic substance of the cytoplasm. In many kinds of eggs, 
according to the investigations of Conklin, Crampton, Calkins, 
Foot and Floderus (31), the yolk is formed first around the 
nucleus and then produced progressively towards the periphery 
of the egg. In these cases it may be supposed that the cyto- 
plasm surrounding the nucleus is directly stimulated by the 
nucleus to produce yolk. In amphibians and many other 
vertebrates the yolk first appears at the periphery of the egg. 
In these cases the nucleus has a less direct influence on the 
yolk formation, and this influence is probably exerted through 
the action of a fluid substance which passes by osmosis through 
the nuclear membrane into the cell-body. The investigations 
that have seemed to show that yolk is derived directly from 
nucleoli, or from chromatin, or from follicle cells, are all open 
to question, and until they have been confirmed by further 
research I shall be inclined to believe that yolk formation 1s 
