THE EVOLUTION OF SEX. 



directly associated with the essential functions of the sexes, 

 are included under the title oi primary sexual characters. 



Of less real importance, though often much more striking, 

 are the numerous distinctions in size, colour, skin, skeleton, and 



Male and Female Bird of Paradise {Paradiscn i/iinor). — From 

 Catalogue of Zoological Museum, Dresden. 



the like, which often signalise either sex. These are termed 

 secondary sexual characters ; for though they will be shown in 



