AN EGG-LAYING MAMMAL Echidna moves with a shuffling gait and walks badly upon the sides of its feet. This is precisely the way in which the Myrmecophaga walks, and in both cases the habit has at least the result of preserving unimpaired the sharp claws so necessary to dig down the foundations of ant-hills. Everybody knows nowadays that this mammal lays eggs. And furthermore as in other egglaying vertebrates, the young, when ready for hatching, has a knob on its snout which enables it to break the shell and emerge into the world. When it does emerge it is still taken care of by the mother, who keeps it in her pouch for certain time, and afterwards allows its out for a run and at stated intervals picks it up again and puts it in the pouch to be fed. When the mother intends to rove far she thinks of her infant and places it securely in a burrow dug for the purpose. It is a very interesting fact that an abundance of termites in various parts of the world has resulted in the modication of such diverse types of animals for their enjoyment. The Echidna was made for the termites, not the termites for the Echidna. BIRDS AND FEATHERS CHAPTER VI Birds HE most uninitiated can recognize without the faintest difficulty the characters that distinguish birds from other animals. But it must not be assumed at once that to define them as feathered bipeds is quite enough. For, to begin with, birds are scaly as well as feathered, thus showing a glimpse, externally visible, of their unquestioned relationship to the lower lying reptiles. The feet are always scaly, in parts at least, and generally entirely so. Anyhow, no creature that is not a bird has feathers or even anything at all approaching to feathers, in nature; and per contra, no bird is without feathers. More than this, all birds possess wings, even the wrongly called Apteryx, which has tiny wings concealed beneath its feathers. The term wing here, it will be observed, does not necessarily mean an organ of flight. Though all birds possess wings, all birds cannot fly. Besides the Apteryx, the ostrich tribe generally are purely cursorial, and so are certain rails and one or two other birds. What is meant by wing in this sense is a fore limb, actually and accurately comparable to the arm of man or the fore legs of a cat, in which the number of fingers is reduced from five to three, and the proportions of the remaining bones is somewhat altered from what is found in reptiles and mammals. This being the case, all birds are bipedal, which is another distinguishing character, though it is THE "FOUR-FOOTED” BIRD very faintly discounted by the fact of the "quadrupedal" movements of the young of the Hoatzin and a few others. No birds have teeth; that is, no living birds, for a few now extinct forms had these structures. Every bird has a horny beak, which in some sense stands in lieu of teeth. It is noticeable that birds have an erect and alert attitude, which contrasts with that of the gloomy reptile. The eyes are clear and open, not closed, except, indeed, during actual sleep, in a drowsy fashion. Hearing as well as sight is well developed, and, indeed, the only sense in which birds are as a rule rather deficient is that of smell; but some experiments have gone far toward showing that after all, birds can detect varying odours rather more accurately than has been supposed. In external form birds are most obviously built upon one common plan. This is recognized in popular parlance by the fact that a given bird is apt to be spoken of merely as a bird, while a mammal is more usually classified roughly; it is spoken of as a cat, or an elephant, etc. The flight of birds, as well as their lightness of movement when hopping upon the ground or among trees, is a characteristic of the group, and is associated with air spaces which ramify among the organs of the body and in the substance of the bones. These air spaces are outgrowths of the lungs ; and while they assist in producing a light frame suitable for flying, must also, one would imagine, improve the respiration of the creatures by bringing air into contact with the entire system. No living reptile or mammal has anything approaching to this aeration of the body. It is possible, however, that certain extinct reptiles, particularly the flying Pterodactyles, had something of the kind; so too had, in the opinion of most, the hopping and often gigantic Dinosaurs of the past. Associated with, and perhaps due to, this is the hotbloodedness of birds. Their temperature is higher ANKLE AND FOOT than that of mammals, and the older authors saw in this physiological likeness a reason for associating together birds and mammals. Every fact of structure, however, contradicts such an association, which is nowadays held by no one acquainted with the facts. But, on the other hand, the nearness of the sprightly, intelligent bird to the sullen and unintelligent lizard has been perhaps a little overrated. The group of birds, in fact, is a group which is quite equivalent to that of reptiles on the one hand and to mammals on the other; but the two first are rather nearer to each other than either are to birds. In fact, the common starting point of both birds and reptiles was, as far as we can see, something in the nature of a very simply organized reptile. To return, however, to our living birds, with which alone we are concerned here. It will be noticed, particularly well in the case of a long-legged bird such as a crane or stork, that when a bird is standing upright it stands upon its toes only. Above the toes, which are either three or four in number, with a few exceptions, such as the ostrich, is a long bone which is not, as might be supposed, the equivalent of our shin bone. This long bone is in reality the ankle bones, plus what are technically termed the metatarsals, i.e. those bones which in ourselves lie between the ankle bones proper and the phalanges or bones of the toes themselves. In the human foot the phalanges are the separated toes, while the metatarsals occupy the greater part of the foot. Birds, therefore, have this region of the foot enormously elongated. But the feature is not absolutely distinctive of them, since even in mammals which walk upon their toes, like the horse, the metatarsals are also long. There are other instances of the same elongation of the middle part of the foot. All birds, so far as is known, lay eggs, from which are hatched in due course young birds that resemble their EGGS AND NESTLINGS parents much more closely than do the newly hatched young of the majority of the Amphibia. No bird is ovoviviparous, as are some reptiles. Moreover, as a very general rule the eggs of birds are not merely dropped promiscuously, but laid, sometimes even in a regular position, in definite nests; these nests are often complex structures of some architectual pretensions. The eggs are for the most part coloured, while the eggs of reptiles are never coloured, but always white. A good many birds also lay white eggs. While a reptile emerges from the egg in the likeness of its parents, the young bird does show some differences from its parents, though these are never of a kind such as to justify the use of the term larva for a newly hatched bird. The only suggestion of a larval form among birds is perhaps the Hoatzin, where the mobile fingers with well developed claws at the ends are organs modified for the purposes of the nestling, and thus just come under the category of what is meant by a larva. All these facts, except perhaps the last, are familiar enough to every one; but it is just as well to emphasize them in order to point out the distinctions between birds and other vertebrated animals. Newly hatched birds differ in different cases. In some species they are completely nude and devoid of feathers. In others they are covered with down, which. is shed by being thrust up upon the tips of the subsequently produced nestling plumage, which itself gives way later to the final and annually deciduous plumage. The twittering and " cheeping" of the young is succeeded in many birds by a most elaborate voice, produced by the movement of a vibrating membrane at the junction of the two bronchi, into which the at first single air tube (trachea), leading to the lungs, divides. More is said of the bird's voice later. In the meantime, it is as well to note that the possession of a voice of the kind which reaches its maximum for |