CELL DIVISION — SPINDLE IN SEA-URCHIN EGGS 233 



The results with KCN lend additional support to the views 

 already expressed on the relation of the mitotic process to the 

 colloidal changes in the cytoplasm. Cyanide acts by intensifying 

 gelation. Hence, as is to be expected, it does not (in moderate 

 concentration) prevent the early stages of mitosis, and develop- 

 ment proceeds as far as the spindle stage. But that particular 

 stage of mitosis which is associated with a reversal of gelation 

 cannot take place in the presence of the cyanide. 



Chloretone acts somewhat like KCN. A 0.08 per cent solu- 

 tion checks segmentation, although it does not markedly injure 

 the eggs. Such a solution intensifies the normal gelation. 



THE NATURE OF THE NORMAL MITOTIC GELATION 



Earlier in this paper I have attempted to show that the ap- 

 pearance of the mitotic figure is necessarily preceded by a cy- 

 toplasmic gelation. Such a gelation can be artificially produced 

 in unfertilized eggs by various reagents, the best of which ap- 

 parently is a hypertonic solution. The question now arises as 

 to how the gelation occurs normally. The fact that its artificial 

 production appears to be best imitated by hypertonic solutions 

 leads to the suggestion that, similarly in the developing egg, gela- 

 tion and consequent formation of astral rays and spindle is 

 initiated by the abstraction of water from the cytoplasm by the 

 growing pronuclei. Some of the early students of artificial par- 

 thenogenesis thought that the essential step in the initiation of 

 development was the abstraction of water from the cytoplasm. 



If the normal gelation is produced by an excessive salt concen- 

 tration, then it should be possible to show that gelation produced 

 artificially by hypertonic solutions behaves like the normal gela- 

 tion. To a certain extent this has been done. When the cyto- 

 plasm of the unfertilized egg is gelatinized by hypertonic solutions, 

 such a gelation can be reversed by ether. On the other hand, 

 ether has no effect in reversing or antagonizing the gelatinizing 

 (or coagulating effect) of acids or of distilled water. Hence of 

 these three types of gelation, that produced by hypertonic solu- 

 tions behaves most nearly like the normal. 



