Origin of Species Variorum

migratory birds, which almost always return to the same district. Consequently each newly-formed variety would generally be at first local, as seems to be the common rule with varieties in a state of nature; so that similarly modified individuals would soon exist in a small body together, and would often breed together. If the new variety was successful in its battle for life, it would slowly spread from a central spot, competing with and conquering the unchanged individuals on the margins of an ever-increasing circle. But to the subject of intercrossing we shall have to return. It may be objected by those who have not attended to natural history, that the long-continued accumulation of individual differences could not give rise to parts or organs which seem to us, and are often called, new. But, as we shall hereafter find, it is difficult to advance any good instance of a really new organ; even so complex and perfect an organ as the eye can be shown to graduate downwards into mere tissue sensitive to diffused light. ↑

It may be worth while to give another and more complex illustration of the action of natural selection. ↑ Certain plants excrete .. sweet juice, apparently for the sake of eliminating something injurious from, their sap: this is effected, for instance, by glands at the base of the stipules in some Leguminosæ, and at the backs of the leaves of the common laurel. This juice, though small in quantity, is greedily sought by insects; but their visits do not in any way benefit the plant. Now, let us suppose that the juice or nectar was excreted from the inside of the flowers of a certain number of plants of any species. ... Insects in seeking the nectar would get dusted with pollen, and would certainly often transport it from one flower to another. The flowers of two distinct individuals of the same species would thus get crossed; and the act of crossing, as we have good rea- son to believe, would produce