Next above the Bird family comes the highest form of all—­the Mammals.  But before we begin our consideration of these high forms, let us take a hasty glance at the “connecting-links” between the Birds and the Mammals.  The lowest forms of the Mammals resemble Birds in many ways.  Some of them are toothless, and many of them have the same primitive intestinal arrangements possessed by the birds, from which arises their name, Monotremes.  These Monotremes may be called half-bird and half-mammal.  One of the most characteristic of their family is the Ornithorhynchus, or Duck-bill, which the early naturalists first thought was a fraud of the taxidermists, or bird-stuffers, and then, when finally convinced, deemed it a “freak-of-nature.”  But it is not a freak creature, but a “connecting-link” between the two great families of creatures.  This animal presents a startling appearance to the observer who witnesses it for the first time.  It resembles a beaver, having a soft furry coat, but also has a horny, flat bill like a duck, its feet being webbed, but also furnished with claws projecting over the edge of the web-foot.  It lays eggs in an underground nest—­two eggs at a time, which are like the eggs of birds, inasmuch as they contain not only the protoplasm from which the embryo is formed, but also 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.