68 THE FIRST PRINCIPLES OF HEREDITY 



Now, from these we can derive ten different kinds of germ- 

 cells, each containing two chromosomes — viz : 



We have now ten different kinds of germ-cells, instead of 

 six, from the same parent. 



Now, in fertilization each such germ-cell unites with 

 another one. We get, therefore, in the former case the 

 possibility of 6 x 6 =36 different kinds of offspring, and in 

 the latter case 10 x 10 ==100 different kinds of offspring. 

 This number rapidly rises with the number of chromo- 

 somes : 



Without Doubling. With Doubling. 



Germs. 

 266 



8,074 



258,670 



8,533,660 



The numbers of possible different offspring are, of course, 

 70 X 70, 266 X 266, etc. We get, therefore, practically an 

 infinite variety of offspring, which accounts for the fact 

 that no two individuals in the world are found to be alike. 



1 1 1. —THEORY OF FERTILIZATION. 



What is the meaning of fertilization ? Why are there 

 two sexes, the union of which is necessary for the propa- 

 gation of all the higher species ? 



The question has been variously answered, and it cannot 

 be said that anything like a satisfactory solution has yet 



