68 THE FIRST PRINCIPLES OF HEREDITY 



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

 cells, each containing two chromosomes viz : 



As before : AB, BC, CD. 

 AC, BD. 

 AD. 



Further: AA. 

 BB. 

 CC. 

 DD. 



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. 



Chromosomes. Germs. Germs. 



8 .. 70 266 



12 . . 924 . . 8,0/4 



16 .. 12,870 .. 258,670 



20 .. 184,756 .. 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. 



III. 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 



