The fancies of men have peopled three of the four so-called elements, earth, air, water, and fire, with strange forms of life, and have even found in the salamander an inhabitant for the fourth. On land the centaur and the unicorn, in the air the dragon and the roc, in the water tritons and mermaids, may be named as instances among many of the fabulous creatures which have been not only imagined but believed in by men of old times. Although it may be doubted whether men have ever invented any absolutely imaginary forms of life, yet the possibility of combining known forms into imaginary, and even impossible, forms, must be admitted as an important element in any inquiry into the origin of ideas respecting such creatures as I have named. One need only look through an illuminated manuscript of the Middle Ages to recognize the readiness with which imaginary creatures can be formed by combining, or by exaggerating, the characteristics of known animals. Probably the combined knowledge and genius of all the greatest zoologists of our time would not suffice for the invention of an entirely new form of animal which yet should be zoologically possible; but to combine the qualities of several existent animals in a single one, or to conceive an animal with some peculiarity abnormally developed, is within the capacity of persons very little acquainted with zoology, nay, is perhaps far easier to such persons than it would be to an Owen, a Huxley, or a Darwin. In nearly every case, however, the purely imaginary being is to be recognized by the utter impossibility of its actual existence. If it be a winged man, arms and wings are both provided, but the pectoral muscles are left unchanged. A winged horse, in like manner, is provided with wings, without any means of working them. A centaur, as in the noble sculptures of Phidias, has the upper part of the trunk of a man superadded, not to the hind quarters of a horse or other quadruped, but to the entire trunk of such an animal, so that the abdomen of the human figure lies _between_ the upper half of the human trunk and the corresponding part of the horse’s trunk, an arrangement anatomically preposterous. Without saying that every fabulous animal which was anatomically and zoologically possible, had a real antitype, exaggerated though the fabulous form may have been, we must yet admit that errors so gross marked the conception of all the really imaginary animals of antiquity, that any fabulous animal found to accord fairly well with zoological possibilities may be regarded, with extreme probability, as simply the exaggerated presentation of some really existent animal. The inventors of centaurs, winged and man-faced bulls, many-headed dogs, harpies, and so forth, were utterly unable to invent a possible new animal, save by the merest chance, the probability of which was so small that it may fairly be disregarded.