Origin of Species Variorum

Comparison with 1872

shaped pieces of bone, apparently representing vertebræ? As Owen has remarked, the benefit derived from the yielding of the separate pieces in the act of parturition by mammals, will by no means explain the same construction in the skulls of birds. Why should similar bones have been created in the formation of the wing and leg of a bat, used as they are for such totally different purposes, namely flying and walking? Why should one crustacean, which has an extremely complex mouth formed of many parts, consequently always have fewer legs; or conversely, those with many legs have simpler mouths? Why should the sepals, petals, stamens, and pistils in any individual flower, though fitted for such distinct purposes, be all constructed on the same pattern?

On the theory of natural selection, we can, to a certain extent, answer these questions. We need not here consider how the bodies of some animals first became divided into a series of segments, or how they became divided into right and left sides, with corresponding organs, for such questions are almost beyond investigation. It is, however, probable that some serial structures are the result of cells multiplying by division, entailing the multi- plication of the parts developed from such cells. It must suffice for our purpose to bear in mind that an indefinite repetition of the same part or organ is the common characteristic, as Owen has remarked, of all low or little specialised forms; therefore the unknown progenitor of the Vertebrata probably possessed many vertebræ; the unknown progenitor of the Articulata, many segments; and the unknown progenitor of flowering plants, many leaves arranged in one or more spires. ↑ We have also formerly seen that parts many times repeated are eminently liable to vary, not only in number, but in form. And as the whole amount of modification will have been effected by slight successive steps, we need not wonder at discovering in such parts, being already present in considerable numbers, and being highly variable, would naturally afford the materials for adaptation to the most different purposes; yet they would generally retain, through the force of inheritance, plain traces of their original or fundamental resemblance. They would retain this resemblance all the more, as the variations, which afforded the basis for their subsequent modification through natural selection, would tend from the first to be similar; the parts being at an early stage of growth alike, and being subjected to nearly the same conditions. Such parts, whether more or less modified, unless their common origin became wholly obscure, would be serially homologous.

In the great class of molluscs, though ... the

shaped pieces of bone? As Owen has remarked, the benefit derived from the yielding of the separate pieces in the act of parturition of mammals, will by no means explain the same construction in the skulls of birds and reptiles. Why should similar bones have been created to form the wing and the leg of a bat, used as they are for such totally different purposes? Why should one crustacean, which has an extremely complex mouth formed of many parts, consequently always have fewer legs; or conversely, those with many legs have simpler mouths? Why should the sepals, petals, stamens, and pistils, in each flower, though fitted for such widely different purposes, be all constructed on the same pattern?

On the theory of natural selection, we can ... answer these questions. In the vertebrata, we see a series of internal vertebræ bearing certain processes; in the articulata, the body divided into a series of segments, bearing external appendages; and in flowering plants, spiral whorls of leaves. ↑ An indefinite repetition of the same part or organ is the common characteristic, as Owen has observed, of all low or little modified forms; therefore ... the unknown progenitor of the vertebrata no doubt possessed many vertebræ; the unknown progenitor of the articulata, many segments; and the unknown progenitor of flowering plants, many leaves arranged in one or more spires. We have formerly seen that parts many times repeated are eminently liable to vary in number and structure. Consequently such parts being already present, and being highly variable, would afford the materials for adaptation to the most different purposes; and they would generally retain through the force of inheritance plain traces of their original or fundamental resemblance. ↑

In the great class of molluscs, though it can easily be shown that the