MUSEUM OF COMPARATIVE ZOOLOGY. 191 



The two stars, or, more exactly, spheres, of the first maturation 

 figure already present a difference which is not diminished as the de- 

 velopment of the egg advances. Not alone that there is a noticeable 

 difference in the magnitude of the two stars, constantly somewhat to the 

 disadvantage of the peripheral one, but, further, there is a sharpness to 

 the limitation of the outer star which is missed in the outline of the 

 central figure. Nor is this attributable solely to the obscuration pro- 

 duced by the rays of light from the deeper star having to traverse a 

 greater mass of granular vitelline substance than do those from the more 

 superficial figure. No doubt that fact enhances the difference, but the 

 primary cause seems to lie in the more complete exclusion of the granu- 

 lar elements of the vitellus from the superficial than from the deeper 

 sphere. In another point, too, these two stars may differ : the rays of 

 the outer star, instead of presenting that rectilinear appearance which 

 characterizes those of the deeper star, appear uniformly curved in a like 

 direction (Fig. 47) when the star is viewed from the animal pole. This 

 spiral arrangement of the radiating fibres of one or the other of the am- 

 phiastral stars is a phenomenon of not uncommon occurrence, and will 

 demand a more extended consideration a little further on. It is a less 

 constant feature of the outer star than the peculiarities previously 

 described. Aside from these differences, there seems to be no noticeable 

 distinction between the two asters or their relations to the portions of 

 the spindle so closely connected with each. There is, however, one 

 feature which very soon makes its appearance, or may perhaps be already 

 detected in a faint degree, — I mean a modification of the form of the 

 superficial sphere, which is accomplished at the expense of the diameter 

 which coincides with the polar diameter of the yolk. To be more exact, 

 however, this flattening in the direction of the animal radius is most 

 conspicuous, if not exclusively apparent, on the outer hemisphere of the 

 superficial aster. It is a modification which increases with the motion 

 of translation which the whole internal figure is destined to undergo 

 along this animal radius ; it is perhaps only one of the physical effects 

 resulting from the motion. 



When this maturation figure is spoken of as though it were something 

 by itself, it is not to be understood that it is a sharply defined object 

 with definite boundaries separating it from the remaining portions of the 

 yolk, but, on the contrary, it should be distinctly stated that at this stage 

 the transition from the maturation figure, on the one hand, to the en- 

 veloping portions of the vitellus, on the other, is quite gradual. 



The latter is characterized by the deutoplasmic elements, which are 



