302 



THE THEORY OF THE GENE 



the flower of the hybrid — pink — is weaker than the red, 

 and if the character affects the gene, the red-producing 

 gene in this hybrid should be diluted by the color of the 

 flower. No such effects here, or elsewhere, have been re- 

 corded. The red and the white genes separate in the pink 

 hybrid without showing any somatic effects. 



Fig. 152. 

 a, Abdomen of normal male ; b, of " abnormal ' ' male ; c, of nor- 

 mal female ; d, of " abnormal " ' female of Drosophila melanogaster. 



The evidence from another source is perhaps even a 

 stronger argument against the theory of the inheritance 

 of acquired characters. There is a race of Drosophila — 

 called abnormal abdomen — in which the regular banding 

 of the abdomen is more or less obliterated (Fig. 152). 

 This condition, in its most extreme form, appears in the 

 first flies that emerge from a culture when the food is 

 abundant and the culture is moist and acid. As the cul- 

 ture gets older and dryer, the flies that emerge become 

 more and more normal in appearance, until at last they 

 cannot be distinguished from wild flies. Here we have a 

 genetic character that is extremely sensitive to the 

 environment. Such characters as these furnish a favor- 

 able opportunity to study the possible effects of the body 

 on the germ-cells. 



If we breed the first hatched flies with very abnormal 



