No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 441 



next the cell membrane gradually disappears ; then the chro- 

 matin granules no longer become colored by any of the stains 

 employed, but become refractive and yellowish. All the chro- 

 matin granules do not lose their affinity for stains simulta- 

 neously, but two or three of them may often remain stained as 

 before, while the remaining granules of the same nucleus may 

 have entirely lost their stain. At this period in the nuclear 

 degeneration we find small masses of these unstaining, yellow- 

 ish granules in the cytoplasm, each mass still preserving the 

 form of a nucleus. Later these individual granules wander 

 apart, or those of several nuclei may partially fuse together to 

 produce a larger mass ; these larger masses of granules are 

 always enveloped by a clear zone of cytoplasm, sometimes of 

 considerable e.xtent, so that they appear to be situated in 

 vacuoles of the cytoplasm. The degeneration stages of these 

 nuclei are most frequent in the cytoplasm, before yolk balls 

 begin to arise in it ; as the latter appear, the remnants of the 

 degenerated nuclei gradually vanish, so that when the cell is 

 filled with the yolk balls all vestiges of these nuclei have 

 vanished. We must suppose that they become assimilated by, 

 or dissolved in, the cytoplasm. These formations, the katabolic 

 changes of degenerating nuclei, can in no way be confounded 

 with stages of yolk development, since the small size, yellowish 

 color, and refrangibility of these granular masses serve to dis- 

 tinguish them sharply from any stage of the yolk balls, even 

 though both are often found in the immediate vicinity of each 

 other. 



The nuclei which are destined to become germinal vesicles 

 increase in size to some extent before nucleoli appear in them ; 

 they now differ from the connective-tissue nuclei, apart from 

 their greater dimensions, in having a relatively greater amount 

 of chromatin and in being regularly spherical or oval in form. 

 The first nucleoli to arise always lie in close contact with the 

 inner surface of the nuclear membrane (Figs. 214, 216, 219, 

 220, 224, 225). They usually appear in the form of a thin 

 disc-shaped mass on the inner surface of the membrane, but 

 there is considerable irregularity in the form of this mass, which 

 may be angular or nearly spherical in outline. At the com- 



