Vertebrates, vol. iii. p. 600.) The gibbons rank among the noisiest of
monkeys, and the Sumatra species (Hylobates syndactylus) is also
furnished with an air sack; but Mr. Blyth, who has had opportunities
for observation, does not believe that the male is noisier than the
female. Hence, these latter monkeys probably use their voices as a
mutual call; and this is certainly the case with some quadrupeds, for
instance the beaver. (5. Mr. Green, in Journal of Linnean Society,
vol. x. Zoology, 1869, note 362.) Another gibbon, the H. agilis, is
remarkable, from having the power of giving a complete and correct
octave of musical notes (6. C.L. Martin, General Introduction to the
Natural History of Mamm. Animals, 1841, p. 431.), which we may
reasonably suspect serves as a sexual charm; but I shall have to recur
to this subject in the next chapter. The vocal organs of the American
Mycetes caraya are one-third larger in the male than in the female, and
are wonderfully powerful. These monkeys in warm weather make the
forests resound at morning and evening with their overwhelming voices.
The males begin the dreadful concert, and often continue it during many
hours, the females sometimes joining in with their less powerful
voices. An excellent observer, Rengger (7. Naturgeschichte der
Saugethiere von Paraguay, 1830, ss. 15, 21.), could not perceive that
they were excited to begin by any special cause; he thinks that, like
many birds, they delight in their own music, and try to excel each
other. Whether most of the foregoing monkeys have acquired their
powerful voices in order to beat their rivals and charm the females or
whether the vocal organs have been strengthened and enlarged through
the inherited effects of long-continued use without any particular good
being thus gained I will not pretend to say; but the former view, at
least in the case of the Hylobates agilis, seems the most probable.
I may here mention two very curious sexual peculiarities occurring in
seals, because they have been supposed by some writers to affect the
voice. The nose of the male sea-elephant (Macrorhinus proboscideus)
becomes greatly elongated during the breeding-season, and can then be
erected. In this state it is sometimes a foot in length. The female is
not thus provided at any period of life. The male makes a wild, hoarse,
gurgling noise, which is audible at a great distance and is believed to
be strengthened by the proboscis; the voice of the female being
different. Lesson compares the erection of the proboscis, with the
swelling of the wattles of male gallinaceous birds whilst courting the
females. In another allied kind of seal, the bladder-nose (Cystophora
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