the
"yolk." on which the embryo feeds until hatched. After the young
Duck-bill is hatched, it feeds from teatless glands in the mother's
body, the milk being furnished by the mother by a peculiar process.
Consider this _miracle_--_an animal which lays eggs and then when her
young are hatched nourishes them with milk_. The milk-glands in the
mother are elementary "breasts."

The above-mentioned animal is found in Australia, the land of many
strange forms and "connecting-links," which have survived there while
in other parts of the globe they have vanished gradually from
existence, crowded out by the more perfectly evolved forms. Darwin has
called these surviving forms "living fossils." In that same land is
also found the _Echidna_ or spiny ant-eater, which lays an egg and then
hatches it in her pouch, after which she nourishes it on milk, in a
manner similar to that of the Duck-bill. This animal, like the
Duck-bill, is a Monotreme.

Scientists are divided in theories as to whether the Monotremes are
actually descended directly from the Reptiles or Birds, or whether
there was a common ancestor from which Reptiles and Birds and Mammals
branched off. But this is not important, for the relationship between
Reptiles, Birds and Mammals is clearly proven. And the Monotremes are
certainly one of the surviving forms of the intermediate stages.

The next higher step in the ascent of Mammal life above the Monotreme
is occupied by the Marsupials, or _milk-giving, pouched animals_, of
which family the opossum and kangaroo are well known members. The
characteristic feature of this family of creatures is the possession of
an external pouch in the female, in which the young are kept and
nourished until they can take care of themselves as the young of other
animals are able to do. The young of the Marsupials are brought forth,
or born, in an imperfect condition, and undeveloped in size and
strength. There are fossil remains of Marsupials showing that in past
ages creatures of this kind existed which were as large as elephants.

In the more common form of Mammals the young are brought forth fully
formed, they having received "nourishment, before birth, from the
mother's body, through the _placenta_, the appendage which connects the
fetus with the parent. The Placental Mammals were the best equipped of
all the life-forms for survival and development, for the reason that
the young were nourished during their critical period, and the car