In characters of such importance as the structure of the hand and foot, the lower apes diverge extremely from the gorilla; thus the thumb ceases to be opposable in the American monkeys, and in the marmosets is directed forwards, and armed with a curved claw like the other digits, the great toe in these latter being insignificant in proportion.
Marmosets are not larger than squirrels, and present great variation in colour; all have long tails, and many have the ears tufted.
It has, however, been proposed to transfer the name Chrysothrix to the marmosets of the genus Hapale, to which it is stated to have been originally applied, and to replace it by Saimiris.
In jerboas, for example, a bunch of twelve or thirteen hairs springs from the same point, while in the polar bear a single stout hair and several slender ones arise together, and in the marmosets three equal-sized hairs form regular groups.
First, the Anthropini, consisting of man only; second, the Catarhini or Old World apes; third, the Platyrhini, all New World apes, except the marmosets; fourth, the Arctopithecini, or marmosets; fifth, the Lemurini, or lemurs; sixth and seventh, the Cheiromyini and Galeopithecini.