62 HARRIETT M. ALLYN. 



nection between the two facts of abnormal mitotic figure and 

 failure of cleavage, whether one or the other is causal, or whether 

 both are caused by the same thing and merely accompany each 

 other, as many think. 



It is certain also that the presence of the normal number of 

 chromosomes in the cleavage nucleus does not insure cleavage. 

 In many cases where only one polar body is extruded the 2 

 number of chromosomes is present, but cleavage does not follow. 

 In the heat experiments, which show the best results that I have 

 obtained, only one polar body, or none, was thrown out, and the 

 2n number appears to be present therefore. Here cleavage was 

 obtained. 



According to R. S. Lillie ('n) the mitotic figure represents 

 an electric field of force, formed because of the more or less 

 sudden increase in permeability at two points on the egg surface, 

 to ions of the opposite sign from those. already determining the 

 sign of the egg protoplasm. In his experiments with Arbacia 

 eggs he found that it was necessary not only to increase the 

 permeability of the membrane in order to induce cleavage, but 

 also to increase it so that the inflow might take place at a certain 

 rate. If this interpretation of cleavage be correct, then it may 

 be that in the case of Chcetopterus the agents which cause dif- 

 ferentiation without cleavage are such as to cause increased 

 permeability, but not w r ith sufficient rapidity to lead to cleavage. 

 Heat, on the other hand, may act by causing more sudden 

 increase. 



If, on the contrary, cleavage be thought of as conditioned, not 

 by electrical phenomena, but by a certain viscosity of the egg, 

 as suggested by Loeb ('92) when he says that the checking of 

 cell-division in a hypertonic solution may be due to a raising of 

 the viscosity of the protoplasm as a result of loss of water, then 

 it seems possible that KC1 and other agents which are thought 

 to extract water from the egg, extract it to so great a degree that 

 the egg is unable to form the cleavage plates because of too great 

 viscosity. 



Normal cleavage requires that certain processes shall take 

 place in correlation. It was evident from the KC1 material 

 that reactions were taking place in the egg which determined 



