Let us look into the subject a little more closely. The common Swift and the common Swallow are birds which intimately resemble one another in many respects. Their size and general coloration are much the same. In both the beak is very broad and short; the first bone of the pointed wing, which corresponds to the human upper arm bone, being also particularly short; whilst the bones of the wing which agree with those of the fore arm—the radius and the ulna—are proportionately very long. In both the feet are small, and the power of progression on the ground feeble, each living almost entirely on the wing, making the smaller insects its staple article of food, and each building its nest in walls or eaves of roofs, not in the branches of trees.
This collection of external resemblances would generally be accepted as sufficient evidence that the Swallow and the Swift are closely allied birds; in other words, that in the pedigree of the bird-class they sprang from a common ancestor, at some, zoologically speaking, comparatively recent time. Further, the fact that the two birds are described next to one another, or placed side by side in collections, by many of those who are in the habit of employing a systematic method of arranging the different genera, would show that such ornithologists consider the relationship between the Swallow and the Swift to be more intimate than that between either of these birds and the Sparrow, Crow, Starling, Lark, &c. But all these last-named birds are what are known as Passerine; in other words, they possess certain anatomical peculiarities in their organization, found in them all, and in no other group of birds. If, therefore, the Swift and the Swallow are more nearly related to one another than either is to any other passerine bird, then, as the Swallow is most certainly passerine, the Swift must be so also.
But certain naturalists assert that the Swift is not a passerine bird at all, and, if they are correct, it is evident that the Swallow and it cannot have anything to do with one another. Upon this assumption, therefore, the passerine Swallow is much more closely related to the Sparrow, the Crow, and the Lark than it is to the Swift.
The question then presents itself—Is it really the case that the importance of the deep-seated anatomical resemblances between the Swallow and the Sparrow, and of the differences between the Swallow and the Swift, is sufficient to justify us, notwithstanding
