MUSEUM OF COMPARATIVE ZOOLOGY. 421 



When any considerable deviation from the spherical form of the fernule 

 pronucleus is noticeable, the latter will, I think, be found to be length- 

 ened rather than shortened along the polar axis of the egg. On the 

 other hand, this flattened condition is quite constant for the corpuscle 

 occupying the centre of the peripheral star of an archiamphiaster.* 



(2.) The position of the "Eikern" is such as to make quite improb- 

 able the interpretation given by Strasburger. It is true that, if a polar 

 globule is not formed here as in the majority of animals (viz. by the 

 division of a spindle body), then we have no right to assume the fulfil- 

 ment of all the conditions which obtain in such a process ; but granting 

 for the moment that here as elsewhere a polar globule is thus formed, 

 then the female pronucleus could hardly have the position close to the 

 surface, as given in the figure, much less the position indicated by the 

 words "pressed against the Hautschicht." The constriction which sepa- 

 rates the two unequal cells — polar globule and yolk sphere — divides 

 the spindle figure approximately in the middle. The interzonal fila- 

 ments must be reduced to zero in order to allow the lateral zone of 

 thickenings to form a new nucleus close to or in contact with the thin 

 cortical layer of the yolk. There is abundant evidence that the zone of 

 thickenings which pertains to the polar globule forms a nucleus in, or 

 beyond, the centre of the polar globule, therefore at some distance fro; a 

 its last formed surface ; f and I recall numerous illustrations which 

 place the corresponding parts of the half-spindle remaining in the yolk 

 at an equal or greater distance from its surface, J — none which place 

 the female pronucleus so close to the surface as in the case of Phallusia, 

 if, perhaps, I make an exception of the case of Hippopodius figured by 

 Hertwig.§ 



If, on the other hand, one takes into account the migration of the 

 spindle as described for Limax, the fact that the corpuscle, a a', occupies 

 a position close to the surface in the stage represented by Fig. 50, and 

 that it ultimately comes to be fused to the apex of the polar globule 

 (Fig. 63), then the interpretation I have given to Strasburger's observa- 

 tions will find, I hope, sufficient justification. I will add a single pecu- 

 liarity further, which, though not prominent, may not be altogether 

 insignificant. 



* Compare for Limax Figs. 43 and 48. See also Whitman's ('78«, pp. 18-21, 

 Fig, 63. C. P. ) account of it as " the pellucid spot." 



t Compare for Limax, Fig. 40 ; also numerous figures by Biitsclili, 0. Hertwig, and 

 others. 



X See Biitschli's figures in Strasburger, op. cit., Taf. VII. Figs. 13, 14. 



§ 0. Hertwig, '78«, p. 186, Taf. IX. Fig. 12 (wrongly numbered " 9 "). 



