ON THE ANATOMICAL CHARACTERS DISTINGUISHING
THE SWALLOW AND THE SWIFT.
By A.H. Garrod, M.A., F.R.S.
It is not a difficult task, whatever the department of the subject which may be under consideration, to classify thinking naturalists in one or other of two divisions, dependent upon the nature of the facts which they, from opportunity or inclination, are in the habit of specially emphasising. There are those who devote themselves to the study of the animal as a whole, its external conformation, its habits, and its haunts. They collect specimens of allied species and preserve them according to an arrangement which is liable to be modified by the experience of collectors generally, and from rumours which reach them as to the results arrived at by those of the class to be referred to immediately. These latter lay but little stress upon superficial resemblance and specific differences, devoting their attention to those facts brought to light by osteological comparison or the differences of deep-seated soft parts, which throw light upon the mutual relations of the larger groups into which the subjects of their study are generally acknowledged to fall.
Now and again the opinions of these two classes of naturalists are apt to be diametrically opposed. The one, as the result of his experience that intimately allied forms closely resemble one another, is apt hastily to draw the illogical conclusion that the converse of the proposition is equally true, and that therefore animals which closely resemble one another in contour and habit must be very nearly related. The other, basing his conclusions on different data, does not run the risk of being misled by the deceptive argument, and forms an opinion which has therefore the average value of his productions.
As an excellent example of the above-mentioned opposed notions of naturalists, the relation of the Swallow to the Swift stands prominently forward. By systematic ornithologists and collectors of birds until recently it has always been the habit to place these birds in juxtaposition, contrary to the opinion of anatomists, just in the same way that the Sand Grouse is grouped by them with the Tetraonidæ, the Petrels with the Gulls, and the Secretary Bird with the Caracaras.
