Passing from the old-world Apes to those of the new world, we meet with
a change of much greater importance than any of these. In such a genus
as 'Cebus', for example (Fig. 17), it will be found that while in some
secondary points, such as the projection of the canines and the
diastema, the resemblance to the great ape is preserved; in other and
most important respects, the dentition is extremely different. Instead
of 20 teeth in the milk set, there are 24: instead of 32 teeth in the
permanent set, there are 36, the false molars being increased from eight
to twelve. And in form, the crowns of the molars are very unlike those
of the Gorilla, and differ far more widely from the human pattern.

The Marmosets, on the other hand, exhibit the same number of teeth as
Man and the Gorilla; but, notwithstanding this, their dentition is very
different, for they have four more false molars, like the other
American monkeys--but as they have four fewer true molars, the total
remains the same. And passing from the American apes to the Lemurs,
the dentition becomes still more completely and essentially different
from that of the Gorilla. The incisors begin to vary both in number
and in form. The molars acquire, more and more, a many-pointed,
insectivorous character, and in one Genus, the Aye-Aye ('Cheiromys'),
the canines disappear, and the teeth completely simulate those of a
Rodent (Fig. 17).

Hence it is obvious that, greatly as the dentition of the highest Ape
differs from that of Man, it differs far more widely from that of the
lower and lowest Apes.

Whatever part of the animal fabric--whatever series of muscles, whatever
viscera might be selected for comparison--the result would be the