106 



HEREDITY AND SEX 



In fact, sight in the sense of forming visual pictures 

 can occur only when eyes are well developed. This 



FIG. 53. Male (to left) with long eye stalks and female (to right) of 

 a fly, Achia longividens. (After Wood.) 



may be taken to score a point in favor of Darwin's 

 hypothesis. 



In the group of insects the most noticeable differences 

 occur in the butterflies and moths, and in flies. A 

 few cases are found in the beetles and bugs. The 

 male cicada's shrill call is supposed to attract the 



FIG. 54. Male to left with horns and female to right without horns of a 

 fly, Elaphomyia. (After Wood.) 



females. The males of certain beetles have horns - 

 the female lacks them (Fig. 52). 



In a genus of flies the eyes are stalked, and the 



