s is the case with some members of
the same order. Why Cercopithecus, considering its habits while young,
has not become thus provided, it would be difficult to say. It is,
however, possible that the long tail of this monkey may be of more
service to it as a balancing organ in making its prodigious leaps, than
as a prehensile organ.

The mammary glands are common to the whole class of mammals, and are
indispensable for their existence; they must, therefore, have been
developed at an extremely remote period, and we can know nothing
positively about their manner of development. Mr. Mivart asks: "Is it
conceivable that the young of any animal was ever saved from destruction
by accidentally sucking a drop of scarcely nutritious fluid from an
accidentally hypertrophied cutaneous gland of its mother? And even
if one was so, what chance was there of the perpetuation of such a
variation?" But the case is not here put fairly. It is admitted by most
evolutionists that mammals are descended from a marsupial form; and
if so, the mammary glands will have been at first developed within
the marsupial sack. In the case of the fish (Hippocampus) the eggs are
hatched, and the young are reared for a time, within a sack of this
nature; and an American naturalist, Mr. Lockwood, believes from what he
has seen of the development of the young, that they are nourished by
a secretion from the cutaneous glands of the sack. Now, with the
early progenitors of mammals, almost before they deserved to be thus
designated, is it not at least possible that the young might have been
similarly nourished? And in this case, the individuals which secreted a
fluid, in some degree or manner the most nutritious, so as to partake of
the nature of milk, would in the long run have reared a larger number
of well-nourished offspring, than would the individuals which secreted a
poorer fluid; and thus the cutaneous glands, which are the homologues of
the mammary glands, would have been improved or rendered more effective.
It accords with the widely extended principle of specialisation, that
the glands over a certain space of the sack should have become more
highly developed than the remainder; and they would then have formed a
breast, but at first without a nipple, as we see in the Ornithorhyncus,
at the base of the mammalian series. Through what agency the glands over
a certain space became more highly specialised than the others, I will
not pretend to decide, whether