Origin of Species Variorum

by the terms, varieties, species, genera, families, &c.; and we have to discover the lines of descent by the most permanent characters whatever they may be and of however slight vital importance. .. ..

The similar framework of bones in the hand of a man, wing of a bat, fin of the porpoise, and leg of the horse,— the same number of vertebræ forming the neck of the giraffe and of the elephant,— and innumerable other such facts, at once explain themselves on the theory of descent with slow and slight successive modifications. The similarity of pattern in the wing and in the leg of a bat, though used for such different purpose,— in the jaws and legs of a crab,— in the petals, stamens, and pistils of a flower, is likewise intelligible on the view of the gradual modification of parts or organs, which were aboriginally alike in an early progenitor in each of these classes. On the principle of successive variations not always supervening at an early age, and being inherited at a corresponding not early period of life, we .. clearly see why the embryos of mammals, birds, reptiles, and fishes are so closely similar, and .. so unlike the adult forms. We may cease marvelling at the embryo of an air-breathing mammals or bird having branchial slits and arteries running in loops, like those of a fish which has to breathe .. air dissolved in water by the aid of well-developed branchiæ.

Disuse, aided sometimes by natural selection, has often reduced organs when they have become useless under changed habits or .. conditions of life; and we can clearly understand on this view the meaning of rudimentary organs. But disuse and selection will generally act on each creature, when it has come to maturity and has to play its full part in the struggle for existence, and will thus have little power .. on an organ during early life; hence the organ will