The gigantic reptile Diplodocus on land.
FOOTNOTE:
[4] The elephant, the thigh-bone of which, measuring nearly 3 ft. in length, is drawn in Fig. 32, is a large Indian one. This species is exceeded in size by the African. See "Science from an Easy Chair," Second series, p. 123.—The largest elephant the bones of which are known is the Elephas antiquus of the Pleistocene, bigger than either of the living species and bigger than the mammoth, Elephas primigenius. The arm-bone (humerus) of one of this species (Elephas antiquus) lately dug up near Chatham and now in the Natural History Museum, is 4 ft. 3 in. in length.
CHAPTER VII
WHAT IS MEANT BY "A SPECIES"?
THOSE who take an interest in natural history must find it necessary to know what the naturalist means by "a species" of animal or plant. What does he mean when he says: "This is not the same species as that," or "This is a species closely allied to this other species," or "This is a new species"? What are the "species" concerning the origin of which Darwin propounded his great theory? There is really no English word which can be exactly used in place of the word "species." I often have to use the word when writing about plants or animals, and should like once for all to say what is meant by it. One might suppose that a "kind" is the same thing as a species. And so it often is; but, on the other hand, by the word "kind" we often mean a group including several species. For instance, we say the "cat-kind" or the "daisy-kind," meaning the "cat-like" animals or the "daisy-like" plants. The expression "the cat-kind" includes the common cat and the wild cat, and even leopards, lions, and tigers, each of which is a species of cat. And by the "daisy-kind" we understand a group including several species of daisies, such as the common daisy, the ox-eye daisy, the camomile daisy, the michaelmas daisy, and others. Hence we cannot translate species simply by the word "kind." "Kind" is the same word as "kin"—"a little more than kin and less than kind," runs Hamlet's bitter pun. "Kind" means a group held together by kinship, and it may be a larger or a smaller group held together by a close kinship or by a more distant one. "Sort," again, will not serve our purpose as an English translation of "species." For, although "a sort" implies a certain selection and similarity of the things included in the "sort," the amount of similarity implied may be very great or it may be indefinitely vague and remote. Hence naturalists have to stick to the word "species," and to use it with a clear definition of what they mean by it.
Suppose we get together a large unsorted collection—many hundred "specimens" or individuals—of the common butterflies of England. Then, if we look them over, we shall find that we can pick out and arrange the specimens into definite groups, according to their colour-pattern. We find that the kinds which we readily distinguish are called in English the swallow-tails, the whites, the sulphurs, the clouded yellows, the tortoise-shells, the peacocks, the red admirals, the painted ladies, the gatekeepers, the meadow browns, the heaths, the coppers, and the blues. There might be others in such a collection, but that is enough for our purpose. On examining the specimens closely, we find that the colour-markings and "venation" or network by which the wings are marked and the shape of the wings, body, and legs of all the specimens of the swallow-tails are almost exactly alike, and unlike those of any of the others. We shall find if we have a dozen or two specimens that there is a slight difference in the pattern, size, and colour of wing of some of the swallow-tails, dividing them into two groups, which we soon ascertain to be the males and females; but this is so small a difference that we may ignore it. The swallow-tail is obviously and at once distinguished from any of the other butterflies in the collection by its colour-pattern and shape. So also with the others, there will be many specimens in each case agreeing in colour and pattern, and recognizable and distinguishable from the rest by the colour-pattern and by the "venation" or "nervures" of the wings. If we collect butterflies again in other years and in other parts of the country, we find the same set of shapes and patterns exactly, corresponding to what we have learnt to call swallow-tails, whites, sulphurs, clouded yellows, tortoise-shells, etc. There are, we thus learn, several distinct, unchanging kinds of butterfly, which are common in this country, and appear every year. Similarly we may go into a meadow in spring, and gather a number of flowers, and a naturalist will roughly arrange our bouquet into "kinds"; there will be the buttercups, the daisies, the clovers, the dead nettles, the poppies, the roses, the orchids, etc.