70 bulletin: museum of comparative zoology. 



considerable length and the elongation of the cytosome is about to begin 

 (Fig. 91). Then the chromatin bodies become scattered throughout the 

 nucleus (Figs. 92, 93, 94). Next they undergo a process of dissolution 

 by which all chromosomic boundaries seem to be broken down (Figs. 95, 

 96, 98, 99). The first stages in this are shown in Figures 95 and 96, 

 where some of the chromosomes have already broken down and the chro- 

 matic material has been deposited in irregular masses upon the linin 

 framework of the nucleus. This change continues to involve more and 

 more of the chromatin until, at the stage represented in Figure 98, the 

 only definite body of chromatin in the nucleus is the karyosphere. 



Soon after this stage the chromatin begins to undergo a still more 

 fundamental change. Already, in the granular condition (Figs. 97, 98), 

 it seems gradually to become dissolved in the hyaloplasm of the nucleus. 

 Stages in this transformation are shown in Figures 99—102. Most of 

 the chromatin seems to become collected into one or more dense, irregular 

 masses of granules at the centre of the nucleus, where it is surrounded 

 by a clear layer of hyaloplasm (Fig. 99). The remainder of the chro- 

 matin occurs in the form of granules or small masses of granules irregu- 

 larly disposed about the peripheral region of the nucleus (Figs. 99, 100). 

 The nuclear sap at this place has not the same character as the more 

 central kai'yolymph, but is very appreciably stained by Congo red 

 (Fig. 99). It is evident that this difference in staiuing is due to 

 the dissolution of the chromatin masses, for as these gradually dis- 

 appear, more and more of the nucleus exhibits this reaction to the stain 

 (Figs. 100, 102). As this process continues, the amount of chromatin 

 staining in the ordinary manner becomes less and less, until at the stage 

 of Figure 102 only a little remains. This stage may be taken as the 

 period of greatest diffusion, for all of the nuclear substance, except the 

 small quantity of unmodified chromatin and a small area immediately 

 surrounding it, assumes a reddish gray color. Thus, while the chromatin 

 which undergoes this chemical change loses its characteristic reaction 

 toward stains, it still shows its presence in the nucleus by the deeper 

 coloration of this entire structure. 



Meantime other changes in the nucleus are taking place. Attention 

 has been called to the fact that, up to the time when the elongation of 

 the cell body is well under way, there is no continuous nuclear mem- 

 brane. Shortly after the acrosome vesicles begin to appeal", however, 

 the nucleus becomes much smaller and a distinct membrane is formed 

 (Figs. 96-99). It is highly probable that the nucleus takes an impor- 

 tant part in the formation of the acrosome, for when the first indications 



