60 sexual selection: birds. part 11, 
more deeply embedded in the adult male than in th® 
female or young male. In the male Merganser tb® 
enlarged portion of the trachea is furnished with 0® 
additional pair of muscles . 45 But the meaning of thew 
differences between the sexes of many Anatidse is n (lt 
at all understood ; for the male is not always the mol® 
vociferous ; thus with the common duck, the male hissed 
whilst the female utters a loud quack . 46 In both sexes 0* 
one of the cranes (Grus virgo ) the trachea penetrate 8 
the sternum, but presents “ certain sexual modifications- 
In the male of the black stork there is also a well' 
marked sexual difference in the length and curvature of 
the bronchi . 47 So that highly important structures ha*® 
in these cases been modified according to sex. 
It is often difficult to conjecture whether the man) 
strange cries and notes, uttered by male birds during 
the breeding-season, serve as a charm or merely as 11 
call to the female. The soft cooing of the turtle-do*® 
and of many pigeons, it may be presumed, pleases th® 
female. "When the female of the wild turkey utters h fc ’ r 
call in the morning, the male answers by a differed 
note from the gobbling noise which he makes, whe ’ 1 
with erected feathers, rustling wings and distended 
wattles, he puffs and struts before her . 48 The spel °* 
the black-cock certainly serves as a call to the female 
for it has been known to bring four or five female 5 
45 Bishop, in Todd’s ‘ Cyclop, of Anat. &n<l Phys.’ voL iv. p. 1409* 
46 eia; spoonbill (Pinto Ji -a) has its trachea convoluted into a flgaf 6 
of eight, and yet this bird (Jordon, ‘ Birds of India,’ vol. iii. p. 768) >' 
mute ; hut Mr. Blyt.li informs me that the convolutions are not co"' 
stantly present, so that perhaps they are now tending towards aborti® 4 *' 
4 ' ‘Elements of Coni]). Anat.’ by B, Wagner, Eng. translat. IS45, P’ 
111. With respect to the swan, as given above, Yarrell’s ‘Hist. ot 
British Birds,’ 2nd edit. 1815, vol. iii. p, 193. 
48 C. L. Bonaparte, quoted in the ‘ Naturalist Library : Birds,’ v® 1, 
xiv. p. 126. 
