BIRDS 141 



flight, and the sound appears to be employed in courtship. 

 Darwin mentions several other cases in which peculiarly 

 modified feathers are used to produce special sounds, such 

 modifications being confined to the males, and the sounds 

 being used in courtship. In the snipes, Scolopax, the outer 

 tail leathers are modified, the shaft being stiff and curved 

 like a sabre. Both sexes are furnished with these feathers, 

 but they are generally larger and produce more sound in the 

 male. The male bird during the pairing season flies to a 

 great height, and then descends in a curved line with great 

 velocity with the tail spread out. The sound is only produced 

 during this rapid descent. In one of the Indian bustards, 

 Sypheotides auritus, the primary wing feathers are narrowed 

 at the tips in the males only, and are probably used to 

 produce a humming sound in courtship. In Ghamoejpetes 

 unicolor, belonging to the Turkey family, the first primary wing 

 feather is arched towards the tip, and narrower than in the 

 female : it is probably used to produce a sound in courtship. 

 In all the above cases it is most probable that the 

 modification of the feather has been directly brought about 

 by the use made of it. I do not mean by this to maintain 

 that the mutilation of a feather can be inherited, such in- 

 heritance seems inconceivable. But particular pressures and 

 strains due to the resistance of the air when certain feathers 

 are moved in a particular way must necessarily cause special 

 pressures and strains on the papilla at the base of the feather, 

 and these mechanical irritations would modify the growth of 

 the feather or of its successor. The feather is not a living 

 tissue, but the papilla and skin to which it is attached are 

 certainly alive, and must be greatly affected by any move- 

 ments of the feather, whether these are produced by the 

 muscles of the skin itself or by the pressure of the air. In 

 this way it is possible to understand why specially modified 

 feathers occur in one sex only which performs special motions 



