THE BIOLOGY OF THE CELL SURFACE 



chemical reactions in the cytoplasm underlie both differen- 

 tiation and heredity. 



In thus relating heredity and the action of the genes to 

 reactions in the cytoplasm, we come to a more physio- 

 logical conception for heredity than the theory of the gene 

 and one which instead of running counter to the facts of 

 differentiation of development is consonant with them. 

 From fertilized egg to the least active cell in the adult 

 organism, the visible manifestations of life are outside the 

 nucleus. It is the cytoplasm therefore that we consider to 

 be the field of activities be they concerned with heredity 

 or differentiation. 



With reactions in the cytoplasm deals the fifth event dur- 

 ing cleavage enumerated above with which our discussion 

 of the cause of differentiation is concerned: the redistribu- 

 tion of water during cleavage. 



From fertilization through cleavage eggs of marine 

 animals certainly and all others probably show a visible 

 altered distribution of water. This is best observed in 

 experimentally treated eggs, but it can also be seen in 

 normal development, as I stated In the chapter on water. 

 After the initial ectoplasmic dehydration which occurs when 

 eggs are fertilized or subjected to experimental means that 

 Initiate development, the egg establishes a new equilibrium 

 with the sea-water. On this level, water, as discrete drops, 

 moves from place to place within the egg or from egg to 

 external medium. The formation of water-drops Is a 

 rhythmical phenomenon which accompanies each division- 

 cycle of the cleavage-period. 



The addition or removal of water In a reversible reaction 

 determines hydrolysis or synthesis, respectively. Thus, 

 water plays a role as a component In chemical reactions; 

 In addition, it is both a solvent for other components and 

 a part of the cytoplasmic structure, the chamber of the 

 reactions. Then the demonstration that water is inter- 



330 



