MUSEUM OF COMPARATIVE ZOOLOGY. 227 



the amphiaster. The central portion of each aster thus becomes some- 

 what lenticular in form. Its outline is less convex on the face, which 

 looks toward the remaining aster of the pair. More or less in con- 

 formity with this change in the shape of the stellar ''areas," the asters 

 themselves are modified from the perfectly spherical appearance which 

 they at first present. The rays are no longer of the same length, nor 

 are they all uniformly tapering. At some distance from the centre is 

 disposed a more or less complete zone of much thicker and more con- 

 spicuous fibres (Figs. 85, 82). These are not thickened throughout their 

 whole extent, but are abruptly enlarged. The enlargements are con- 

 tinued for a distance equal to the breadth of the zone, when they are 

 as abruptly reduced to the ordinary dimensions. These zones are not 

 of uniform prominence on all sides of the aster, but in places gradually 

 fade away. 



The central area of each stellate figure may remain for some time 

 homogeneous (Fig. 85, aa) ; at length there appear within it, however, 

 groups of highly refractive granules (Fig. 82), which, with the flattening 

 of the area, assume a corresponding distribution, so that when seen in 

 profile they have an irregular linear arrangement. When the stellate 

 figures have attained this complication of structure (Fig. 82), the pro- 

 nuclear bodies are no longer recognizable as distinct structures. All 

 that is left to indicate their previous existence are numerous dark gran- 

 ules irregularly arranged midway between the two asters, and, in a region 

 that is now traversed by stellar rays, a few very faint circular outlines 

 (pnl ?) of a size corresponding to that of the pronucleoli in the stage 

 just preceding. The indistinctness of these circular outlines prevents 

 that certainty which one feels in regard to the existence of the dark 

 granules, and this mistrust is increased by the appearances presented by 

 other eggs (Figs. 86 - 89), where there is found a trace of the nucleus of 

 the first cleavage sphere, but where there is no evidence of any contained 

 nucleolar bodies. Notwithstanding this apparent contradiction, I am 

 inclined to believe that occasionally the pronucleoli may in part persist 

 even after the disappearance of the outline of the pronucleus, and after 

 its substance has become so diff'used as to be no longer readily distin- 

 guishable from the surrounding vitelline substance. 



The dissolution of both these structures — the pronuclear membrane 

 and the pronucleoli — doubtless falls within a very limited extent of 

 time, and it may not be wrong to infer that in one instance the disap- 

 pearance of the one precedes, whereas in another case the disappearance of 

 the other first takes place. A trace of the nuclear substance has even been 



