COURTSHIP AMONG BIRDS 127 



of girders to form supports for the now membranous 

 chamber walls. Some species seem to show that this 

 fenestration has been pushed to excess, leaving only 

 vestiges of this singular chamber, as is shown in PI. 21. 

 In some species the bronchi are much swollen, and the 

 syringeal chamber has entirely disappeared : in others, 

 as in the Merganser and Goosander, a large syringeal 

 chamber is supplemented by dilatations of the windpipe. 



Save in the case of the Goosander, these peculiar 

 structures are found only in the male, but in the species 

 first named the male, in addition to the syringeal chamber, 

 has two fusiform swellings in the windpipe, one above 

 the other : in the female one of these swellings is 

 present, but there is no syringeal box. 



This box is generally, and probably correctly, regarded 

 as a sort of musical instrument. Nevertheless the males 

 are far less vociferous than the females which have no 

 such voice resonator. One has only to listen to, and 

 compare the notes of the Mallard drake and duck to 

 discover this fact. Here, then, we seem indeed to have 

 a case of " Hypertely." Before, however, we build too 

 much on this we must discover whether the sibilant sounds 

 uttered by the males do, or do not, play an important 

 part in arousing the sexual passions of the females. 



Certain of the Swans and Cranes afford illustrations 

 of musical instruments of an even more remarkable kind. 

 Herein the windpipe at the base of the neck enters a 

 large chamber formed by the absorption of the diploe 

 sandwiched between the outer walls of the keel of the 

 breastbone and the enlargement of the space so created 

 until it can accommodate the tubular windpipe. This, 

 entering the cavity in the form of a loop, runs the whole 

 length of the keel, the upper limb of the loop finally 



