27 
though they rarely ascend beyond the limit of the fig-trees. 
All day long they haunt the tops of the tall trees; and 
though, towards evening, they descend in small troops to 
the open ground, no sooner do they spy a man than they 
dart up the hill-sides, and disappear in the darker valleys. 
All observers testify to the prodigious volume of voice pos- 
sessed by these animals. According to the writer whom I 
have just cited, in one of them, the Siamang, “the voice is 
grave and penetrating, resembling the sounds goek, goek, 
goek, goek, goek ha haha ha haaaaa, and may easily be heard 
at a distance of half a league.” While the cry is being uttered, 
the great membranous bag under the throat which commu- 
nicates with the organ of voice, the so-called “laryngeal sac,” 
becomes greatly distended, diminishing again when the crea- 
ture relapses into silence. 
M. Duvaucel, likewise, affirms that the cry of the Siamang 
may be heard for miles—making the woods ring again. So 
Mr. Martin* describes the cry of the agile Gibbon as “ over- 
powering and deafening ” in a room, and “ from its strength, 
well calculated for resounding through the vast forests.” Mr. 
Waterhouse, an accomplished musician as well as zoologist, 
says, “The Gibbon’s voice is certainly much more powerful 
than that of any singer I ever heard.” And yet it is to be 
recollected that this animal is not half the height of, and far 
less bulky in proportion than, a man. 
There is good testimony that various species of Gibbon 
readily take to the erect posture. Mr. George Bennett,t a 
very excellent observer, in describing the habits of a male 
Hylobates syndactylus which remained for some time in his 
possession, says; “ He invariably walks im the erect posture 
when on a level surface ; and then the arms either hang down, 
enabling him to assist himself with his knuckles; or what is 
more usual, he keeps his arms uplifted in nearly an erect 
position, with the hands pendent ready to seize a rope, and 
* “ Man and Monkies,” p. 423. 
{ Wanderings in New South Wales, Vol. IL. chap. viii. 1834. 
