districts whence blow the strongest and most prevalent winds; and the modifications they have undergone are largely dependent upon the nature of the other species with which they have to compete, or to whose habits they must needs accommodate themselves. In such cases it is easy to see how far Darwin's special conception of natural selection helps to explain and account for facts not easily explicable by the older evolutionism of mere descent with modification. Embryology, the study of early development in the individual animal or plant, also throws much side light upon the nature and ancestry of each species or family. For example, gorse, which is a member of the pea-flower tribe, has in its adult stage solid, spiny, thorn-like leaves, none of which in the least resemble the foliage of the clover, to which it is closely related; but the young seedling in its earliest stages has trefoil leaves, which only slowly pass by infinitesimal gradations into flat blades and finally into the familiar defensive prickles. Here, natural selection under stress of herbivorous animals on open heaths and commons has spared only those particular gorse-bushes which varied in the direction of the stiffest and most inedible foliage; but the young plant in its first days still preserves for us the trefoil leaf which it shared originally with a vast group of clover-like congeners. The adult barnacle, once more, presents a certain fallacious external resemblance to a mollusk, and was actually so classed even by the penetrating and systematic intellect of Cuvier; but a glance at the larva shows an instructed eye at once that it is really a shell-making and abnormal crustacean. On a wider scale, the embryos of mammals are at first indistinguishable from those of birds or reptiles; the feet of lizards, the hoofs of horses, the hands of man, the wings of the bat, the pinions of birds, all arise from the same fundamental shapeless bud, in the same spot of an almost identical embryo. Even the human foetus, at a certain stage of its development, is provided with gill-slits, which point dimly back to the remote ages when its ancestor was something very like a fish. The embryo is a picture, more or less obscured and blurred in its outline, of the common progenitor of a whole great class of plants or animals.