70 



SEX 



We should also note, after a survey of 

 sex-characters, that conspicuous difference 

 between the sexes is the exception, and general 

 similarity the rule. In many of the higher 

 animals the males and females are very like 

 one another in external appearance. Cat, 

 mouse, rabbit and hare, may be mentioned 

 among mammals ; rook, kingfishers, and 

 many parrots among birds. Below the level 



FIG. 14. The sexes in a small fish Phallostethus dunckeri. 

 The female (F) is the larger. The male (M) bears a re- 

 latively large intromittent organ projecting below the 

 gill-cover. (After C. Tate Regan.) 



of crustaceans, in animals like starfishes and 

 sea-urchins, marine worms, thread-worms, 

 jellyfish and corals, it is rare to find more than 

 minute sex-dimorphism. 



THE GENERAL CONTRAST. Contrariwise, 

 although there may not be any marked 

 dimorphism, there may be a profound func- 

 tional difference. There are many facts, long 

 since summarised in The Evolution of Sex, 

 which go to show that the metabolism of 

 the male and the female are very different. 



