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 



-:r;v^-^; 



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 



