SURFACE TENSION AND CELL-DIVISION 



239 



or when the egg divides into two equal blastomeres, it is 

 necessary to provide the surface of the two systems with free 

 energy. Hence, during cell-division the egg must do work 

 in order to provide free surface energy. 



Before proceeding further with this argument, let us consider 

 the effect of altering the surface tension at the protoplasmic/ 

 water interface during the actual process of cleavage. In order 

 to do this, eggs at different stages of cleavage are transferred 



Text-fig. 4. 



c d 



Stages in the fusion of two oil-drops. 



to acid and alkaline sea-water. In the latter case division 

 occurs quite normally ; in the former case striking effects 

 are produced. 



The effects of acid sea-water may be summarized as follows : 



(i) The cleavage furrow is entirely lost, and in the early stages 

 of cleaA^age the egg tends to become spherical in form. 



(ii) In the total abolition of the cleavage furrow there is 

 distinct evidence that the egg is elongated along the main 

 axis of the astral figure, so that in the latter stages of cleavage 

 the form of the egg is that of a well-marked cylinder with 

 hemispherical ends. 



(iii) The effect of acid sea-water is entirely reversible. If an 

 egg which has been taken from normal to acid sea-water be 



