species which have it most perfectly formed it is very long and
powerful, and the end has the underside covered with bare skin, exactly
resembling that of the finger or palm of the hand and apparently equally
sensitive. One of the common kinds of monkeys that accompany street
organ-players has a prehensile tail, but not of the most perfect kind;
since in this species the tail is entirely clad with hair to the tip,
and seems to be used chiefly to steady the animal when sitting on a
branch by being twisted round another branch near it. The statement is
often erroneously made that all American monkeys have prehensile tails;
but the fact is that rather less than half the known kinds have them
so, the remainder having this organ either short and bushy, or long
and slender, but entirely without any power of grasping. All
prehensile-tailed monkeys are American, but all American monkeys are not
prehensile-tailed.

By remembering these characters it is easy, with a little observation,
to tell whether any strange monkey comes from America or from the Old
World. If it has bare seat-pads, or if when eating it fills its mouth
till its cheeks swell out like little bags, we may be sure it comes from
some part of Africa or Asia; while if it can curl up the end of its tail
so as to take hold of anything, it is certainly American. As all the
tailed monkeys of the Old World have seat-pads (or ischial callosities
as they are called in scientific language), and as all the American
monkeys have tails, but no seat-pads, this is the most constant external
character by which to distinguish them; and having done so we can look
for the other peculiarities of the American monkeys, especially the
distance apart of the nostrils and their lateral position.

The whole monkey-tribe is especially tropical, only a few kinds being
found in the warmer parts of the temperate zone. One inhabits the Rock