lerican Museum or Natural Historj 



SECONDARY SEXUAL CHARACTERS AMONG BIRDS 

 The drab female and gay male, African ostrich 



some of these secondary sexual characters are found even among the water- 

 inhabiting fishes and some of the crustaceans and other invertebrates, as well 

 as in all classes of vertebrates (see illustrations, p. 391). 



Here we see again a certain resemblance between maleness or femaleness 

 in the individual and the special characteristics of the gametes. There is the 

 roving disposition of the male, for example, as against the passivity of the 

 female, or the contrasting aggressiveness and receptivity of the two sexes. 

 These differences are associated in more complex animals with differences in 

 nerves and muscles, in sense-organs and the effectors. 



Among birds, we are impressed by the extravagant plumage of the peacock, 

 in contrast with the plain garb of the peahen. In the bird of paradise and in 

 the domestic fowl, the flashy dress and ornaments of the male are accompanied 

 by show-off behavior and song. The spurs are related to a fighting temper. 

 Among mammals, the males seem to go in for beards and ferocious-looking 

 manes, for horns and large teeth. In many species there is a great difference 

 in size between the sexes, the male being generally larger and more belligerent 

 (see illustrations above and opposite). 



The floral displays of seed -bearing plants and the specialized spore- 

 distributing and spore-catching adjustments are so varied that they have 

 occupied the Ufelong study of many devoted scientists and nature-lovers. 

 When the facts about seed-bearing plants are described, as they often are, by 



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