434 MONTGOMERY. [Vol. XV. 



are first produced, but a varying number are formed simultane- 

 ously and at different parts of the cell ; it is usually, though 

 not always, the case that they first arise at the periphery of the 

 cell at some distance from the nucleus. The mature yolk 

 globules are slightly larger than these and stain somewhat 

 more intensely, which shows that they gradually become denser 

 as they increase in size ; in the largest ova these spherules 

 are so abundant that the true cytoplasm is quite obscured 

 (Fig. 247). 



First nucleolar stage. — In the smallest nuclei found there is 

 a peripheral group of several nucleoli lying close to the nuclear 

 membrane, which are spherical in form (Figs. 236-238). 



Second nucleolar stage. — The nucleoli have increased in num- 

 ber, and, departing from their original peripheral position, now 

 occupy the center of the nucleus (Figs. 239 and 240). So small 

 are they, and so densely grouped may they become, that at 

 first sight one might be led to suppose that each group of 

 numerous nucleoli was a single nucleolus. In those cases 

 where the nucleus is oval or elongated in form, instead of 

 spherical (the usual case), in the place of a single cluster two 

 are commonly present, or else the single mass or cluster of 

 nucleoli is elongate in shape, its outline being more or less par- 

 allel to the contour of the nucleus. The nucleoli in this stage 

 are always more numerous and usually also smaller than those 

 of the previous period ; their increase in number might thus 

 be brought about, in part at least, by divisions of the earlier 

 nucleoli. 



Third nucleolar stage. — The nucleus now is much larger, 

 and the nucleoli begin to wander apart towards the periphery 

 of the nucleus (Figs. 241, 243, 246, 247). I have observed all 

 stages between nuclei containing centrally grouped, small 

 nucleoli and those in which they have come to lie close to the 

 nuclear membrane. In this stage, as in the preceding one, 

 the nucleoli are perfectly homogeneous without vacuoles, and 

 spherical in form. In a few nuclei, however, they appear 

 greatly vacuolated, but these cases are so rare that they must 

 be considered abnormal. At the end of this period they attain 

 their greatest dimensions, though they thereby become some- 



