development and dominance in the animal world. Why he stopped short
of the higher brain development I cannot tell. The fact remains that
the mammal is pre-eminent in brain power, and that this gave him the
supremacy.

But mammals came very late to the throne, and the probability of
their ever gaining it must for ages have appeared very doubtful.
They seem to have been a fairly old group with a very slow early
development. Reptiles especially, and even birds, were far more
precocious than these slower and weaker forms which crept along the
earth. But reptiles and birds, like many other precocious children,
soon reached the limit of their development. They had muscle, the
mammal brain and nerve; the mammal had the staying power and the
future. Bitter and discouraging must have been the struggle of these
feeble early mammals with their larger, swifter, and more powerful,
reptilian relatives. And yet, perhaps, by this very struggle the
mammal was trained to shrewdness and endurance.

The primitive mammals laid eggs like reptiles or birds. Only two
genera, echidna and platypus, survive to bear witness of these old
oviparous groups, and these only in New Zealand. These retain
several old reptilian characteristics. Their lower position is shown
also by the fact that the temperature of their bodies is, at least,
ten degrees Fahrenheit below that of higher mammals. One of these
carries the egg in a pouch on the ventral surface; the other, living
largely in water, deposits its eggs in a nest in a burrow in the
side of the bank of the stream.

After these came the marsupials. In these the eggs develop in a sort
of uterus; but there is no placenta, in the sense of an organic