The Descent of Man

In some birds the vocal organs differ greatly in
the two sexes. In the Tetrao cupido (Fig. 39) the
male has two bare, orange-coloured sacks, one
on each side of the neck; and these are largely
inflated when the male, during the breedingseason,
makes his curious hollow sound, audible
at a great distance. Audubon proved that
the sound was intimately connected with this
apparatus (which reminds us of the air-sacks
on each side of the mouth of certain male
frogs), for he found that the sound was much
diminished when one of the sacks of a tame
bird was pricked, and when both were pricked
it was altogether stopped. The female has "a
somewhat similar, though smaller naked space
of skin on the neck; but this is not capable of
inflation." (41. 'The Sportsman and Naturalist in
Canada,' by Major W. Ross King, 1866, pp. 144-
146. Mr. T.W. Wood gives in the 'Student'
(April 1870, p. 116) an excellent account of the
attitude and habits of this bird during its
courtship. He states that the ear-tufts or neck-