MUSEUM OF COMPARATIVE ZOOLOGY. 207 



vitelline substance. This in itself might have been a serious argument 

 against interpreting it as the second archiamphiaster, had I not already 

 shown from Fig. 23 the possibility of such a state of affairs. The 

 V centres of the stellate figures do not exhibit distinctly outlined " areas," 

 and the radiate fibres consequently become gradually lost in the central 

 darl^er portion. 



I have spoken of the spindle ; this exists potentially rather than for- 

 mally. The substance lying between the two asters is much clearer 

 than the surrounding protoplasm, that is, it is destitute of vitelline 

 granulations. Its outline, though not sharp and definite, is sufficiently 

 distinct to show that it has an almost spherical figure, tapering a little 

 at the poles. The fibres which help to make it conspicuous are not large, 

 nor are they evenly distributed through its substance. A view along 

 its axis (Fig. 54) shows that it is only the peripheral portion of the 

 spindle which is thus differentiated, and, further, that it is not devel- 

 oped alike on all sides. While the fibres on one side extend a third 

 of the way toward the axis, on the opposite side they form only a thin 

 layer. No median or lateral zones of thickenings are observable. 



The impression conveyed by these observations is that the spindle 

 is not yet completed, that it is rather in process of formation, and that 

 the differentiation, commencing at the surface, advances with varying 

 rapidity toward the axis of the figure. If it were absolutely certain 

 that this is the second archiamphiaster, there would be little ground for 

 the belief that it was formed by a simple elongation of the half-spindle.* 



In Fig. 55 the amphiastral figure has assumed a strictly radial po- 

 sition, and the peripheral star has already reached the surface of the 

 vitellus, where it induces a prominent protuberance. The inequality 

 of the two asters is more noticeable than in the formation of the first 

 polar globule, a phenomenon which must be prevalent if the superficial 

 asters and the resulting polar globules are proportional in size. What 

 seems most peculiar in the outer star is the limited extent of the radial 

 influence on the side toward the centre of the vitellus, a feature not seen 

 in other figures at this stage. f The deeper star remains central in posi- 



* There is hardly reason to suppose that the egg seen at Fig. 53 is so far advanced 

 as to present the amphiaster of the first cleavage sphere. Neither the stage of 

 development, as inferred from eggs of the same lot, nor the position of the figure 

 nor the inequality of the stars, seem reconcilable to such an interpretation. 



t As indicated by a previous reference to this figure, the external aster presents 

 m a marked degree, when viewed from the animal pole, the peculiar spiral arrange- 

 ment of its radiate fibres which was seen in an early stage of the formation of the first 

 polar globule. 



