THE VITAL PHENOMENA OF THE CELL 



241 



rest, they reappear, and division proceeds as usual. If, however, the 

 substances are allowed to act upon the eggs for from 10 to 20 

 minutes, a still greater disturbance is produced, resulting in many 

 cases in a very peculiar and, in its way, typical course of the division 

 process. Not only are the pole radiations completely destroyed, but 

 the nuclear segments become gradually transformed into the vesi- 

 cular resting condition of the nucleus (Fig. 129 A). This constitutes 

 the starting point of a new but considerably modified process of 

 division (0. and R. Hertwig VI. 38). 



Fio. 129. Nuclei of eggs of Strongylocentrotus which, one and a half hours after the act 

 of fertilisation has occurred, have been placed in - 025 per cent, solution of quinine sulphate, 

 where they remained for twenty minutes. A Nuclear figure of an egg, which was killed one 

 hour after it was removed from the quinine solution ; B nuclear figure of an egg, killed 

 somewhat later; nuclear figure of an egg, killed two hours after it was removed from 

 the quinine sulphate solution. 



Instead of two radiations, four develop immediately upon the 

 surface of the nuclear vesicle (Fig. 129 _B, in which one radiation 

 is obscured). If treated with quinine, these soon become sharply 

 defined ; when, however, chloral is used, they remain permanently 

 faint, and confined to the immediate neighbourhood of the nucleus. 

 The nuclear membrane next becomes dissolved ; five spindles de- 

 velop between the four poles, and upon these the nuclear seg- 

 ments distribute themselves equatorially, thus producing a cha- 

 racteristic figure (Fig. 129 G). The nuclear segments then move 

 towards the four poles, and form the basis for four vesicular 

 nuclei, which separate from one another and travel towards the 

 surface of the yolk. The egg then begins, by means of two cross 

 furrows, to become constricted into four corresponding segments. 



However, as a rule, this division into four portions is not com- 

 pleted until after the four nuclei have begun to make preparations 

 for dividing again by forming spindles with two pole radiations. 



