eeds
them at the breast.

But there is a gradual advance in this process. The Duckbill lays its
eggs just like the reptile, but provides a warm nest for them at the
bottom of its burrow. The Anteater develops a temporary pouch in its
body, when it lays an egg, and hatches the egg in it. The Marsupial
retains the egg in its womb until the young is advanced in development,
then transfers the young to the pouch, and forces milk into its mouth
from its breasts. The real reason for this is that the Marsupial falls
far short of the higher mammals in the structure of the womb, and cannot
fully develop its young therein. It has no placenta, or arrangement by
which the blood-vessels of the mother are brought into connection with
the blood-vessels of the foetus, in order to supply it with food until
it is fully developed. The Marsupial, in fact, only rises above the
reptile in hatching the egg within its own body, and then suckling the
young at the breast.

These primitive mammals help us to reconstruct the mammal life of
the Mesozoic Epoch. The bones that we have are variously described
in geological manuals as the remains of Monotremes, Marsupials, and
Insectivores. Many of them, if not most, were no doubt insect-eating
animals, but there is no ground for supposing that what are technically
known as Insectivores (moles and shrews) existed in the Mesozoic. On
the other hand, the lower jaw of the Marsupial is characterised by a
peculiar hooklike process, and this is commonly found in Mesozoic jaws.
This circumstance, and the witness of Australia, permit us, perhaps,
to regard the Jurassic mammals as predominantly marsupial. It is more
difficult to identify Monotreme remains, but the fact that Monotremes
have survived to this day in Australia, and the resemblance of some
of the Mesozoic teeth to those found for a time in the young Duckbill
justify us in assuming that a part of the Mesozoic mammals correspond to
the modern Monotremes. Not single specimen of any higher, or placental,
mammal has yet been found in the whole Mesozoic Era.

We must, however, beware of simply transferring to the Mesozoic world
the kinds of Monotremes and Marsupials which we know in nature to-day.
In some of the excellent "restorations" of Mesozoic life which are found
in recent illustrated literature the early mammal is represented with an
external appearance like that of the Duckbill. This is an error, as the
Duckbill has been greatly modified in its