62 THE THEORY OF THE GENE 



a different end-product. In fact, the change not only af- 

 fects the eyes, but other parts of the body as well. The 

 sheath of the testes is colorless, while it is greenish in 

 red-eyed flies. The white-eyed flies are more sluggish 

 than their red-eved fellows, and have a shorter life. It 

 is probable that many parts of the body are affected by 

 the change that took place in some part of the germinal 

 material. 



At rare intervals, lighter colored, or pale individuals, 

 of the currant moth, Abraxas, appear in nature. They 

 are females as a rule. A pale, mutant female bred to a 

 dark, wild type male (Fig. 39) gives offspring that are 



Fig. 40. 

 The mutant character Lobe* of D. melanogaster. The eyes are 



small and protruding. 



like the dark type. These, inbred, give the old and the new 

 types as 3 to 1. Pale F 2 individuals are all females. If 

 they are bred to males of the same generation, some 

 pairs give pale males and females, as well as dark types 

 in equal numbers. From the former a pale stock can be 

 reared. 



The two preceding mutant characters act as recessives 

 toward the corresponding character in the wild type, but 

 other mutants act as dominants. For example : lobe 2 is 

 characterized by the peculiar shape and size of the eye 

 (Fig. 40). It arose as a single individual. Half of its off- 



