The evolving of wings meant much to the ascending forms of life. The Reptiles were compelled to live in a narrow circle of territory, while the Birds were able to travel over the earth in wide flights. And travel always develops the faculties of observation, memory, etc., and cultivates the senses of seeing, hearing, etc. And the creature is compelled to exercise its evolving "thinking" faculties to a greater extent. And so the Birds were compelled by necessity of their travels to develop a greater degree of thinking organism. The result is that among birds we find many instances of intelligent thought, which cannot be dismissed as "mere instinct." Naturalists place the Crow at the head of the family of Birds, in point of intelligence, and those who have watched these creatures and studied the mental processes, will agree that this is a just decision. It has been proven that Crows are capable of counting up to several figures, and in other ways they display a wonderful degree of almost human sagacity.

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.

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.