522 BULLETIN OF THE 



minative vesicle ; and even if it did show this, it would not follow that 

 such a position could not have been effected by the invasion of an aster- 

 bearing protuberance of vitelline protoplasm, in the manner described by 

 Hertwig. 



There are no accounts by other authors in which the centre of the 

 aster is shown to lie within the nucleus, — none in which it is not pos- 

 sible to suppose that the protoplasm surrounding the nucleus takes at 

 least an equal share in the formation of the asters. From the cases given 

 above it will be sufficiently clear that the converse of this proposition 

 does not hold true. So far, then, as regards the origin of asters, I hold 

 that they are primarily phenomena of the protoplasm rather than of the 

 nucleus. I do not wish, however, to deny to the nucleus the possibility 

 of any influence in their production, but must insist that the immediate 

 cause of their appearance is not of necessity a iRorpliologically persistent 

 part of the nucleus. 



The male aster appears to present the most serious obstacle to this 

 view of the origin of molecular stars. If it be granted that they are 

 essentially like other asters, it may pertinently be asked what evidence 

 there is that the star is not due to the direct influence of the nuclear 

 substance (male pronucleus), toward the centre of which its rays are di- 

 rected. From my own observations on Limax I should hardly be able 

 to give any satisfactory reply ; the only asters which I should feel justi- 

 fied in referring to the influence of the male element are those which 

 occur in the single abnormal case described. The short rays are there 

 directed toward central corpuscles, which I have assumed to be equiva- 

 lent to the male pronuclei seen by other observers, so that the evidence, 

 little as it is, would be unfavorable to the view I have adopted. But 

 Fol's {'77", p. 465) observation above alluded to may possibly off'er an 

 explanation of the difficulty, and ultimately prove that the male aster 

 is, after all, only an apparent exception. Fol states that in Sagitta, dur- 

 ing the motion of the male pronucleus toward the female, it is very evi- 

 dent that the centre of the star (male aster) is in advance of the clear spot 

 (male pronucleus), and that the latter is drawn on in a passive manner. 

 The figures which 0. Hertwig has given of the pronuclei and their asters 

 in Sagitta do not, it is true, directly confirm this observation, but the 

 pear-shaped outline of the pronuclei, when compared with similar forms 

 which are shown in Limax (Fig. 68) to be probably due to the attrac- 

 tion of an aster, is sufficient to suggest the possibility that this peculiar 

 contour in Sagitta has been produced by a like cause. Unfortunately, 

 Fol has not stated whether the pronucleus suffers any change of form as 



