32 PROBLEMS OF FERTILIZATION 



Our purpose, however, is to focus on the moment of 

 fertihzatioji itself, feeling sure of the great significance 

 of any adequate analysis of such an event. Even so 

 doing, we are dealing with a highly complex situation 

 in which all of our knowledge of the morphology and 

 physiology of cells is requisite for a statement of the 

 problems. 



The biologist who surveys the stupendous panorama 

 of sex in the plant and in the animal kingdom must 

 feel that there is a universal biological significance of 

 fertilization, in terms of either function or composition. 

 By some biologists emphasis has been laid on the aspect 

 of rejuvenation and by others on the mingling of the 

 parental germ plasms as a source of diversity and vari- 

 ation within the species — on amphimixis, in brief. 



The development of an organism after a very early 

 stage is characterized by decreasing rate of metabolism; 

 that is to say, at a certain early stage, which will be more 

 •fully defined later, the organism possesses its maximum 

 growth energy, which, in the case of a mammal for 

 instance, may be more than a hundred times that 

 possessed at birth. The growth energy decreases from 

 its maximum point most rapidly at first, with in- 

 creasingly diminishing rate until full growth is attained. 

 Thereafter the processes of growth and destruction prac- 

 tically balance, for a time, up to old age and death. 



Charles S. Minot deserves the credit for first clearly 

 defining these principles in a quantitative way. He 

 showed that in the early stages of embryonic develop- 

 ment, from the ninth to the fifteenth day of gestation, 

 rabbits add 704 per cent to their weight daily, and 

 inferred that in yet earlier stages the rate of in- 



