184 bulletin: museum of comparative zoology. 



the growing oocyte when the chromatin has lost its distinctly spireme- 

 like form and is becoming rearranged into a more delicate granular 

 reticulum. In this stage the nucleolus maintains the affinity for dyes 

 that it first had, while the nuclear reticulum behaves as follows : with 

 hematoxylin-eosin the original bluish color becomes purple or reddish; 

 with picro-hematoxylin somewhat less blue, though never yellow; 

 with acid fuchsin-methyl green mixtures the reticulum, at first de- 

 cidedly green, becomes bluish or even red. At about the end of the 

 growth period, when the nuclear reticulum presents the appearance 

 of finely divided and uniformly scattered granules, the entire nucleus 

 may stain very uniformly. Apparently at this time there is either only 

 a slight chemical difference between the linin and chromatin constitu- 

 ents, at least so far as our stains give evidence, or else the physical 

 condition of the nuclear ingredients is the cause of the uniformity of 

 staining. 



The changes which the nucleolus undergoes are either a gradual 

 decrease in size, or a fragmentation, or both. The time at which 

 these changes begin, relative to the size of the growing egg, varies 

 considerably ; sometimes they start almost as soon as the egg begins 

 its growth, at other times only at a later period, after considerable 

 growth. Figure 39 shows the nucleus of an oocyte w^hich has grown 

 to three or four times its original diameter; the nuclear reticulum 

 stains rather faintly; the nucleolus has already decreased in size and 

 is composed of two pieces; in picro-hematoxylin the larger stains 

 yellowish, the smaller bluish, about like the reticulum. Figure 40b 

 possibly represents a later stage or, perhaps, a slightly different method 

 of the breaking up of the nucleolus. Instead of the detachment of 

 one large mass, there has been a separation of several smaller ones. 

 This oocyte is of about the same size as the one belonging to the nucleus 

 shown in Figure 39, and the staining reactions are the same. The 

 decrease in the size of the nucleolus becomes evident by a comparison 

 with the nucleolus of an adjacent oocyte nucleus shown in Figure 40a. 

 There are evidences that the nucleolus loses this substance in a liquid 

 form, since the main mass remains of regular shape and sharp outline, 

 while the detached parts suggest, by their form and position, that they 

 are flowing along the network of the nucleus. A larger oocyte is 

 represented by its nucleus in Figure 41, where, besides a single nucleo- 

 lus with a vacuole, there are several smaller bodies of nucleolar origin 

 distributed in the reticulum. The nucleus in Figure 42, from an 

 oocyte grown to one-quarter of its final size, has several similarly 

 staining nucleolar bodies in close contact with one another. Figure 



