MUSEUM OF COMPARATIVE ZOOLOGY. 197 



fibres are of nearly the same length. Consequently the inner limita- 

 tion of this outer aster — the surface which abuts upon the granular 

 vitellus — is, as before, of nearly circular outline ; the free or exposed 

 portion, on the other hand, has not quite the form of the arc of a circle, 

 for the curvature is sharpest at a point directly over the centre of radia- 

 tion. The course of the adjacent rays is nearly parallel with this outline. 

 The whole figure of the outer star is thus changed from a sphere to a 

 form more resembling a biconvex lens, with its more highly curved 

 surface directed outward. 



The compact body which in the earlier stages existed at the centre of 

 radiation still persists, although its form is further modified by a con- 

 tinued . flattening. It is in the profile view that this body is most con- 

 spicuous. It corresponds, I believe, with that which Robin ( '75, p. 34) 

 calls in Nephelis " un espace clair circulaire, superficiel," but which has 

 been better seen and more clearly depicted by Whitman ( '78^, p. 18, 

 and Figs, 62, 63, C. P.), in the case of Clepsine. I shall have occa- 

 sion to recur to this subsequently. 



The modifications which the external aster has undergone, caused in 

 part at least by its relation to the outer envelope of the vitellus, do 

 not find their counterpart in a like modification of the deeper aster. 

 A certain amount of change may also be observed here. This aster 

 has also approached the animal pole; it has moved to a position at 

 some distance from the centre of the vitellus; there is also a slight 

 change in the extent of the radiate influence of which it is the expres- 

 sion, for the rays which reach out into the vegetative hemisphere are 

 somewhat longer than those belonging to the opposite half of the yolk. 

 Its peripheral limitation continues to be less sharply marked than that 

 of the outer star. The inner ends of the rays, on the other hand, 

 terminate at a nearly uniform distance from the centre of radiation. 



The spindle itself still retains the robust proportions characteristic of 

 the earlier stages. Its length has not suffered appreciable change, and 

 its outline is less modified at the equator than in the earlier stages, 

 when the bending at this place often appeared quite abrupt. The inter- 

 stellate fibres are more distinct than formerly, and the centres of the 

 stars continue to be the points of convergence for the two extrem- 

 ities of the spindle fibres. The thickenings of the latter are more or 

 less widely separated, and appear as two distinct and conspicuous 

 zones at equal distances from the equator. When seen lengthwise of 

 the spindle, the numerous (40 to 50) thickenings appear arranged — 

 more distinctly than in the previous stage — in the form of a ring. 



