XXIII 

 THE ACTION OF THE SPERMATOZOON UPON THE EGG 



II. THE COMBINATION OF ARTIFICIAL PARTHENOGENESIS AND 

 FERTILIZATION WITH SPERM IN THE SAME EGG 



1. Two possibilities exist for the explanation of the activa- 

 tion of the egg by a spermatozoon: either the spermatozoon 

 carries a ferment or a catalyzer into the egg which accelerates 

 the rate of the chemical reactions in the egg; or it removes an 

 obstacle to the development. The rdle of the membrane forma- 

 tion favors the latter idea, since it is not conceivable that all 

 the diverse means by which development can be induced act 

 as ferments; moreover, they only act provided they cause the 

 membrane formation. Hence the membrane formation is the 

 essential factor which induces development at least in the sea- 

 urchin egg. This makes it rather improbable that the sperma- 

 tozoon induces development by carrying a catalyzer into the 

 egg (although it may carry enzymes for other purposes, e.g., 

 heredity). 



This idea is supported by other facts. We know that the 

 velocity of chemical reactions is increased if the quantity of 

 the catalyzer is increased; and that if we double the quantity 

 of the catalyzer the rate of velocity is increased in the ratio 

 of either 1:2 or l:i/2. The rate of chemical reactions during 

 development can be measured by the rate of cell division of the 

 egg, as is evidenced through the influence of temperature upon 

 the rate of development (chap. iii). Hence if the spermatozoon 

 'caused development by carrying a catalyzer into the egg, the 

 rate of segmentation should be either twice as fast or 1 .4 times 

 as fast if two spermatozoa enter the egg as if only one sper- 

 matozoon enters. As is well known, cases occur in which two 

 spermatozoa enter the egg. In such cases the egg divides into 



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