c, ui>. xviii. 
VOCAL 0 LiGANS. 
277 
f loes not believe that the male is more noisy than the 
female. Hence, these latter monkeys probably use their 
v °ices as a mutual call; and this is certainly the case 
"‘th some quadrupeds, for instance with the beaver. 5 
Another gibbon, the H. agilis, is highly remarkable, 
fe°m having the power of emitting a complete and 
c °iTeet octave of musical notes, 6 which we may reasonably 
Sl) spect serves as a sexual charm ; but I shall have to 
d-'ciir to this subject in the next chapter. The vocal 
0| 'guns of the American Mycetes caraya are one-third 
Wgep in the male than in the female, and are wonder- 
felly powerful. These monkeys, when the weather is 
'"tom, make the forests resound during the morning and 
Evening with their overwhelming voices. The males 
fe-gin the dreadful concert, in which the females, with 
their less powerful voices, sometimes join, and which 
18 often continued during many hours. An excellent 
observer, llengger, 7 could not perceive that they were 
ex oited to begin their concert by any special cause ; he 
thinks that like many birds, they delight in their own 
'dUsic, and try to excel each other. Whether most of the 
foregoing monkeys have acquired their powerful voices 
lri order to beat their rivals and to charm the females — 
° r whether the vocal organs have been strengthened 
ail d enlarged through the inherited effects of long-con- 
t'uued use without any particular good being gained 
P'1 will not. pretend to say; but the former view, at 
feast in the case of the Hylobate s agilis, seems the most 
Probable. 
I may here mention two very curious sexual pecu- 
harities occurring in seals, because they have been sup- 
Mr. Green, in 1 Journal of Linn. Soc.’ vol. x. Zoology, 18G9, p. 3G2. 
6 C. L. Martin, ‘ General Introduction to the Nat. liist. of Mamin, 
finals, ’ 1841, p. 431. 
' Naturgeschicllte der Saugethiere von Paraguay,’ 1830, s. 15, 21. 
