142 THE TOWER MENAGERIE. 
single spark of intelligence, the gradations are regular 
and easy. A remarkable circumstance connected with 
the developement of this faculty, or perhaps we should 
rather say, with its gradual extinction, consists in the fact 
that it is only in young animals which have not yet 
attained their full growth, that it is capable of being 
brought into play; the older individuals, even of the 
most tractable races, entirely losing the gaiety, and with 
it the docility, of their youth, and becoming at length as 
stupid and as savage as-the most barbarous of the tribe. 
The Monkeys of the Old and of the New World differ 
from each other in several remarkable points, some of 
which are universally characteristic of all the species of 
each, while others, although affording good and tangible 
means of discrimination, are but partially applicable. 
Thus the nostrils of all the species inhabiting the Old 
World are anterior like those of man, and divided only 
by a narrow septum. In those of the New World, on 
the contrary, they are invariably separated by a broad 
division, and consequently occupy a position more or 
less lateral. In the former again the molar teeth are 
uniformly five in number, crowned with obtuse and 
flattened tubercles; while in the latter they are either 
six in number, or in the few anomalous cases in which 
they, are limited to five, and which are peculiar to a 
group that ought to occupy an intermediate station 
between the Monkeys and the Insect-eating Carnivora, 
their crowns are surmounted by sharp and somewhat 
elevated points. The tails of all the American Monkeys 
are of great length, but they differ more or less from 
each other in the power of suspending themselves by 
means of that organ, a faculty which is nevertheless 
