448 WESLEY R. COE, 



its two portions. At this stage the fibres are much elongated below, 

 but are shorter on the side towards the egg- nucleus. In the stage 

 represented in Fig. 25 the process of differentiation has been carried 

 much farther, and those fibres which pass towards the egg-nucleus 

 are very short and delicate, while those on the opposite side of the 

 asters are exceedingly elongated and very coarse. They are no longer 

 straight and smooth but have become very irregularly twisted and 

 bent in various directions. They are also much branched peripherally, 

 and reach within a short distance of the surface of the egg throughout 

 the whole of its lower hemisphere. 



While this massive development of the aster-fibres has been taking 

 place, however, the centrospheres have not only failed to increase in 

 size but have lost their outlines entirely, so that the minute centro- 

 somes seem to lie free in the cell-protoplasm (Fig. 26). And the 

 aster-fibres no longer come to a sharp focus about the centrosomes 

 but radiate rather from the area in which both centrosomes are 

 situated. The fibres are much more delicate in the vicinity of the 

 centrosomes than farther away. Indeed, their inner portions often 

 become so faint that it is impossible to determine where they end, 

 and some terminate much nearer the centrosome than others. This 

 gives an unsymmetrical appearance to the whole figure. 



As the germ-nuclei draw nearer together the aster-fibres become 

 even more massive, especially in their peripheral portions (Figs. 26, 27). 

 They have now attained their maximum development and, in fact, it 

 would be physically impossible for them to become much longer, since 

 they now reach almost to the periphery of the cell (Fig. 27). The 

 two asters are not always, nor indeed are they often equal in size. 

 For, having their centres in close proximity to the germ-nuclei, when 

 these latter are eccentrically situated, as is usually the case, one of 

 the asters will be nearer the periphery of the cell than the other, 

 and its field for growth will be consequently more limited. This in- 

 equality is well shown in Fig. 26, where it is somewhat more marked 

 than usual. In Fig. 27 the asters are much more nearly equal in size, 

 and a conspicuous decussation of the fibres is seen above the germ-nuclei. 



Let us now consider briefly the development of the germ-nuclei 

 themselves up to this stage. The egg-nucleus, as we have seen above, 

 was formed from the sixteen chromosomes remaining in the egg after 

 the formation of the second polar body. This nucleus was at first 

 very small and irregular, but as it sinks more deeply into the body 

 of the cell, it becomes of larger size and acquires a more regular 



