436 MOA'TGOMERY. [Vol. XV. 



classed as germinal vesicles, yet it seems so probable tliat the 

 substance out of which the nucleoli are formed is extranuclear, 

 that I would conclude, a priori, that no nucleoli are present 

 in stages of the germinal vesicle much earlier than those which 

 have been here described. Those small nucleoli of a second 

 generation, which are first produced in the third and fourth 

 nucleolar stages, may represent yolk globules assimilated by 

 the nucleus, since in these stages the cytoplasm is filled with 

 such globules. 



On the other hand, the yolk cannot be considered as having 

 its origin in nucleoli which have wandered out of the nucleus, 

 since in none of these stages are nucleoli found in the cyto- 

 plasm. And if such were the case, one certainly should be 

 able to observe the large nucleoli of the third nucleolar stage 

 in the cell substance, for it is at this period that the yolk first 

 appears. I conclude that the yolk globules have their origin 

 in some substance contained in the cytoplasm, and that the 

 nucleolar substance also has its origin in some cytoplasmic 

 substance. But whether the primitive nutritive substance of 

 the yolk globules and that from which the nucleolar substance 

 is derived are identical, is of course open to question ; how- 

 ever, judging from the similarity in appearance, we might con- 

 clude that the primitive cytoplasmic substance was the same 

 in both cases, and especially if we consider, which seems plaus- 

 ible, the nucleoli to represent the nutritive substance of the 

 nucleus, as the yolk globules certainly represent that of the 

 ■cell body. 



In the first nucleolar stage the nuclear membrane is usually 

 very thin, but always perceptible ; in the later stages it becomes 

 thicker. The nucleus is never noticeably irregular or amoe- 

 boid in outline. Might this be explained by the absence of 

 yolk balls in the cytoplasm .'' 



In the second and at the beginning of the third nucleolar 

 stages, the central mass of nucleoli is usually surrounded by a 

 clear space, in which space few or no chromatin microsomes 

 occur, though it may be transversed by a few achromatic fibers 

 (Figs. 239 and 240). This space was found in most of the egg 

 cells of this stage in the three individuals sectioned, though it 



