28 



HEREDITY AM) SEX 



of tne mallard duck has a green head and a reddish 

 breasl Fig. L6), while the female is streaked with brown. 

 h, insects the males of some species of beetles have 

 hornsOD the head that are lacking in the female (Fig. 

 17 . The males of many species of butterflies are col- 

 ored differently from the females. 



FlO. 11. — White-booted humming bird, two males 

 and (me female. (After Gould.) 



The phosphorescent organ of our common firefly, 

 Phot in us pyralis, is a beautiful illustration of a second- 

 ary sexual character. On the under surface of the male 

 there arc two bands and of the female there is a single 

 band that can be illuminated (Fig. 18). At night the 

 males leave their concealment and fly about. A little 

 later the females ascend to the tops of blades of grass 



