238 Chas. W. and G. T. Hargitt. 



eggs (fig. 26) the reticulum is more complex, fine-meshed and 

 granular, and the chromatin is in a large number of granular, less 

 dense masses. The diffusion of the chromatin does not go beyond 

 this condition, a marked contrast to what happens in Hydro- 

 medusae. In certain of the latter it has been found that charac- 

 teristically the chromatin becomes so finely divided and so diffused 

 that a stage is reached in which the nucleus appears to be without 

 chromatin, though it is still present and later becomes more evi- 

 dent. While the reticulum in Aurelia will select an acid dye, the 

 larger, denser masses always stain with the basic dye; hence 

 the germinal vesicle never has quite the cytoplasm-like appear- 

 ance that it does in nearly mature eggs of Hydromedusse, Near the 

 end of the growth period the granular m? sses of chromatin under- 

 go a process of condensation, leading to the assumption of a more 

 definite shape (fig. 27), straight or twisted strands, loops and 

 rings, considerably smaller than the original chromatin masses. 

 During the progress of these changes the nuclear membrane has 

 become wrinkled, the egg has reached its maximum size, the nucleo- 

 lus is degenerating; it is therefore clear that the time for the 

 formation of polar bodies is near at hand and the chromatin changes 

 described are the beginning of chromosome formation. In the 

 eggs of many animals the chromatin rings and loops become chro- 

 mosomes arranged in tetrads, in Aurelia these are apparently 

 absent in the maturation spindles (fig. 28, 29). 



Maturation 



The first stages in the formation of the maturation spindle 

 were not found, unless figure 26 is one such stage. Here a sin- 

 gle small aster centres in two granules (centrosomes) which have, 

 perhaps, just divided. If this be the beginning of the spindle it 

 is certainly precocious, for the egg is not full grown and the chro- 

 matin and nucleolus are in an earlier stage than in figure 27 ; but 

 in the latter and other similar eggs there is no indication of asters 

 or centrosomes. Whatever the genesis of the spindle, it is at 

 first tangentially placed, as shown in the figure of the incomplete 

 spindle, (fig. 28). Figure 29, a polar view of the first maturation 



