COURTSHIP AND SEX 2ii 



elongated, often peculiarly shaped, feathers which are dis- 

 played, and of brilliant coloration which depends largely 

 on the physical structure of the surface of the feathers. In 

 his" Naturalist in Nicaragua," Belt described the behaviour 

 of two males belonging to the species Florisuga mellivora, 

 which were displaying before a female sitting on a branch. 

 First one and then the other shot up into the air and 

 descended slowly with the white tail so much expanded that 

 •it covered more space than the rest of the bird. Darwin 

 mentions the interesting case of Aithurus polytmus, where 

 the male has brilliant coloration and two immensely long 

 tail-feathers, both characters appearing in the young bird. 



The dimorphism of Game-birds is familiarly illustrated 

 in the case of the common cock and hen, and what we see 

 in the poultry yard has its counterpart in the ancestral 

 Jungle-fowl {Gallus bankiva) of India. The cock is dis- 

 tinguished by longer tail-feathers, longer and brighter neck 

 feathers, larger comb and wattles, and a spur on the inside 

 of each leg. He is polygynous and combative, and he does 

 not share in the care of the young. Mr. Cunningham refers 

 the elongation of the tail-feathers to their movements in 

 courtship, the elongation of the neck hackles to their erection 

 in fighting, the vascular comb and wattles to pecking by the 

 beaks of other birds, and the spur to the doughty blows 

 delivered on the legs and heads of rivals. As we shall after- 

 wards explain, there are many difficulties, to our mind 

 insuperable, in the way of this direct Lamarckism. We 

 regard all these dimorphic features as the outcome of germinal 

 variations and their subtle sifting. 



In birds the sex dimorphism is mainly concerned with 

 plumage and such skin out-growths as combs and wattles, 

 but the variety is nevertheless extraordinary. From the 

 long list we may select a few examples. The male sheld- 

 drake {Tadorna tadorna) has a red knob at the base of the 

 bill, unrepresented in the female, and at the same place the 

 male Wattle-Duck of Brazil, Sarcidiornis carunculata, has a 

 black comb or caruncle, enlarged at the breeding season and 

 absent from the female. The male Tragopan pheasant 



