MUSEUM OF COMPARATIVE ZOOLOGY. 439 



off of the conical protuberance to form the polar globule begins, half in 

 the latter and half in the superficial layer of the yolk. The radiation 

 has meantime diminished, especially in the polar globule, where there is 

 to be seen only a very indistinct arrangement of the protoplasm around 

 a dark granule, the peripheral apex of the spindle. 



I can only confirm for Li max this description, which agrees in every 

 essential particular with what I have seen. In one point, however, I 

 have been less successful than Hertwig. I have not seen the continua- 

 tion of the spindle fibres to the centre of the clear astral area. I observe, 

 moreover, that Hertwig has not uniformly represented the apex of the 

 spindle as occupying the centre of this astral area (e. g. the deep end of 

 the spindle, loc. cit., Taf. II. Fig. 2). 



Of the lateral zones of thickenings Hertwig adds that they appear, 

 when viewed lengthwise of the spindle, as two circles (not rings) of shin- 

 ing granules. About two hours intervene in Nephelis between the cor- 

 responding stages in the formation of the two polar globules. The 

 changes transpiring during this interval, as I have elsewhere indicated, 

 have hitherto eluded most, if not all observers.* 



This hiatus in his observations was recognized by Hertwig, for he 

 says (p. 27) this point — the formation of the second spindle — has 

 remained obscure. According to the ordinary course of nuclear division 

 the half of the spindle which remains in the yolk should at first be con- 

 verted into a homogeneous nucleus, and only then elongate. Some 

 of his preparations also seem to favor the justice of this conclusion ; 

 namely, those where the granules of the semi-spindle remaining in the 

 egg had imbibed nuclear fluid and formed small vacuoles. As other 

 intermediate stages were wanting, Hertwig did not feel able to deny the 

 possibility of a completion of the spindle in a more direct manner, f 



phenomena, especially not to the separation of the halves of the nuclear disk. This 

 is at once evident, I think, from his own figures, as well as from those I have given 

 of Limax. Compare Fig. 40 with Fig. 43. 



* It is true Fol ['IT, p. 448) allows the second spindle to arise by a simple length- 

 ening of the half of the spindle fibres remaining in the yolk, and an elongation of the 

 fibre thickenings; but this conclusion may perhaps not be considered as authoritative 

 and final until it has been shown that intermediate stages cannot have been over- 

 looked. Figures of such intermediate steps as will be a certain guaranty against 

 mistake have not, I believe, been published. There is the more reason for not giving 

 his conclusions too great prominence in this matter, since he aflSxes so little impor- 

 tance to the spindle fibres, and has in the work just cited figured for the first time in 

 his writings their thickenings. 



t It may not be quite irrelevant to notice that the intervals which here elapse 

 between the formation of the two polar globules on the one hand, and between the 



