CAUSE OF HYBRID VIGOR 



175 



ured. It attains this same development, however, by the 

 operation of a different set of factors distributed in the 

 three chromosomes and numbered 2, 4, 6 ; 8, 10, 12 ; and 

 14, 16, 18 in the diagram. Both individuals are homo- 



X: 6 



Y:6 



X X Y : 12 



Via. 36. — To show hoir f aotors contributed by eaoh parent may enable the first generation 

 of a croBB to obtain a greater development than either parent. 



zygous ; i.e., the allelomorphic pairs are composed of like 

 elements. It is also assumed that all these nine factors 

 are as fully effective i aJihe haplo id as in the diploid co n:, 

 dition ; in other words, they show perfect TJominance over 

 their absence. It will be seen from the diagram that when 

 these individuals are crossed together the progeny de- 



