THE BIOLOGY OF THE CELL SURFACE 



the naturally occurring process, differ in their course of 

 development, we know certainly that by either fertilization 

 or parthenogenesis, if development is complete, an adult 

 animal emerges through a succession of nuclear and cyto- 

 plasmic divisions. Therefore, despite any differences that 

 may occur during the developmental process, the beginning 

 stage is always that of the establishment of the cleavage 

 figure with consequent nuclear and cytoplasmic division, 

 the end-stage always being the adult form. The question 

 thus arises as to the nature of the calling forth of 

 the nuclear configuration through whose subsequent 

 rhythmical behavior together with cytoplasmic cleavage 

 the end-stage is attained. The initial action of spermato- 

 zoon and of experimental means being different, and dif- 

 ferences in action obtaining between one means and another, 

 the question at issue is: Do these differences persist so that 

 the calling forth of the process of nuclear and cytoplasmic 

 divisions springs from various causes, or do these means, 

 whatever they are, elicit the same reaction which sets 

 up the division-process ? I suggest that they set up the 

 same reaction.^ Let us briefly review the experimental 

 findings. 



In sea-water sufficiently hypertonic to induce develop- 

 ment, eggs of any species which respond to such treatment 

 rapidly and directly lose water. The minimum hyper- 

 tonicity capable of calling forth development in sea-urchins' 

 eggs does not bring about a sharply defined shrinkage of the 

 eggs from their vitelline membranes; only in stronger hyper- 

 tonic solutions does this egg shrink from its membrane. 

 Other eggs shrink in hypertonic solutions to such an extent 

 that the vitelline membranes no longer adhere to the cyto- 

 plasmic surface. On return to normal sea-water, the eggs 

 take up water but they do not regain the equilibrium with 



1 See Just, ig2Ja. 



242 



