CHAPTER VH 

 THE PROBLEM OF ACTIVATION 



The egg may be activated, caused to develop, either 

 by fertilization or by various artificial means that 

 produce parthenogenesis. Fertilization involves also 

 the factors of specificity and of heredity, but experi- 

 mental parthenogenesis deals with activation alone, and 

 by virtue of variety of methods has become a most 

 instructive method of studying this problem. 



Two phases of activation are readily distinguished. 

 In the first of these the plasma membrane and cortex 

 of the egg are affected; in the second the internal 

 protoplasm, and finally the nucleus, are affected, leading 

 up to a karyokinetic process, the first cleavage of the 

 egg. The outstanding fact in activation of the egg is 

 that it is a process which begins in the cortex and 

 extends toward the center. Activation is usually con- 

 sidered "incomplete" if it does not terminate in a 

 normal cleavage, but there may be different reasons 

 for such "incompleteness." 



I. ACTIVATION BY THE SPERMATOZOON 



The point of view from which analysis must begin 

 is the fact, demonstrated by experimental partheno- 

 genesis, that the egg is an independently activablc 

 system. The old idea that the spermatozoon supi>lies 

 organs or substances necessary for activation must there- 

 fore be abandoned. The egg possesses all substances 



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