III ANIMAL LIFE IN THE TROPICAL FORESTS 307 
liarities. They differ somewhat in dentition and in other 
structural features from all Old World apes, and a consider- 
able number of them have prehensile tails, a peculiarity never 
found elsewhere. In the howlers and the spider monkeys 
the tail is very long and powerful, and by twisting the 
extremity round a branch the animal can hang suspended as 
easily as other monkeys can by their hands. It is, in fact, a 
fifth hand, and is constantly used to pick up small objects 
from the ground. The most remarkable of the American 
monkeys are the howlers, whose tremendous roaring exceeds 
that of the lion or the bull, and is to be heard frequently at 
morning and evening in the primeval forests. The sound is 
produced by means of a large, thin, bony vessel in the throat, 
into which air is forced; and it is very remarkable that this 
one group of monkeys should possess an organ not found in 
any other monkey or even in any other mammal, apparently 
for no other purpose than to be able to make a louder noise 
than the rest. The only other monkeys worthy of special 
attention are the marmosets, beautiful little creatures with 
crests, whiskers, or manes, in outward form resembling squirrels, 
but with a very small monkey-like face. They are either 
black, brown, reddish, or nearly white in colour, and are the 
smallest of the monkey tribe, some of them being only about 
six inches long exclusive of the tail. 
Bats 
Almost the only other order of mammals that is specially 
and largely developed in the tropical zone is that of the 
Chiroptera or bats, which becomes suddenly much less plenti- 
ful when we pass into the temperate regions, and still more 
rare towards the colder parts of it, although a few species 
appear to reach the Arctic circle. The characteristics of the 
tropical bats are their great numbers and variety, their large 
size, and their peculiar forms or habits. In the East those 
which most attract the traveller’s attention are the great fruit- 
bats, or flying-foxes as they are sometimes called, from the 
rusty colour of the coarse fur and.the fox-like shape of the 
head. These creatures may sometimes be seen in immense 
flocks which take hours to pass by, and they often devastate 
the fruit plantations of the natives. They are often five feet 
