154 



SEXUAL DIMORPHISM 



female. They are, however, used to give blows, and from my 

 point of view that is the principal fact. 



Charadriidcc. In the male of the common Peewit, 

 Vanellus cristalus, the tubercle on the wrist of the wing 

 becomes more prominent during the breeding season, and the 

 males fight with their wings, that is to say the tubercle is 

 the result of the blow on the wings. 



In Lobivanellus a similar tubercle becomes developed 

 during the breeding season into a short, horny spur. In 

 L. lobatus of Australia both sexes have spurs, but they are 

 much larger in the males than in the females. 



In Hoplopterus awnatus the spurs do not increase in 

 size during the breeding season, but the males fight with 

 them. 



These weapons resemble in position and function the 

 exostoses of the Solitaire, and support the conclusion that 

 the mechanical irritation is the cause of the growth, more 

 especially when we see that the structures wax and wane 

 in the individual with the periodical increase and decrease 

 in the stimulation. 



In the Herons there is often a summer or breeding 

 plumage, but it is usually alike in both sexes, and both sexes 

 take part in incubation. 



Scolopacidce. Among the Scolopacidae or Snipes, Machetes 

 pugnax, the Ruff affords one of the most convincing instances 

 of the connection between erection and movement of plumes 

 and their excessive growth. The males and females migrate in 

 separate flocks, and remain separate throughout the winter. 

 In the spring, in their northern breeding places, the males 

 fight together and acquire their breeding plumage, which is 

 chiefly distinguished by the ruff of long neck-feathers. These 

 are erected in combat. It is curious that the colours of the 

 plumage of the males should be so remarkably various, 

 scarcely two individuals being alike, but in the development 



