THE RELATIONS OF THE SEXES 155 



aquila during the time that he was engaged in the exploration 

 of Christmas Island (Indian Ocean) . 



" About the beginning of January," he remarks, " the adult 

 males begin to acquire [a] remarkable pouch of scarlet skin 

 beneath their throat. This they can inflate till it is nearly as 

 large as the rest of the body, and a dozen or more of these 

 birds sitting on a tree with outstretched drooping wings and 

 this great scarlet bladder under their heads are a most remark- 

 able sight. When a hen-bird approaches the tree the males 

 utter a peculiar cry, a sort of ' wow-wow-wow-wow ' and clatter 

 their beaks like castanets, at the same time shaking the wings. 

 When they take to flight the air is allowed to escape from the 

 pouch, but occasionally they might be seen flying with it partly 

 inflated." 



This pouch, it should be remarked, is not formed by inflating 

 the gullet, but, as in the case of the Ruffed-grouse, by certain 

 enlarged air-sacs of the cervical system. 



Two other instances of inflatable pouches and the role they 

 play in courtship must suffice for the purposes of this chapter. 



The first of these is that furnished by the Great Bustard 

 {Otis tarda), a bird at one time common on the heaths of 

 England. 



The pouch in this bird is a quite remarkable structure, 

 being formed by a long sac running down the front of the neck 

 just beneath the skin, and opening above by a narrow slit just 

 beneath the free end of the tongue. Its walls are extremely 

 delicate, and just between the furcula are constricted, as may 

 be seen in 111. 21. How it is filled is not yet known, but the 

 performance of the bird after the work of inflation is completed 

 is remarkable. 



The neck is then drawn downwards and backwards so as 

 to rest on the back, while the tail is raised and drawn forwards. 



Unlike so many of the displays already described, that 

 of the Great Bustard is apparently addressed very directly 

 to the female. Approaching her with a mincing gait and 

 rustling wings, he draws the neck backwards and downwards 

 till it rests upon the back, while the tail is raised and drawn 

 forwards and downwards, and is there held in place by the aid 

 of the tips of the long quill feathers of the wings. Simul- 

 taneously the scapular feathers are set on end, and with these 



