Common groundsel is also a case of the same kind; but here the degradation has not gone nearly so far. I venture to conjecture, therefore, that groundsel has been embarked for a shorter time upon its downward course. For evolution is not, as most people seem to fancy, a thing which used once to take place; it is a process taking place around us every day, and it must necessarily continue to take place to the end of all time. By family the groundsel is a daisy; but it has acquired the strange and somewhat abnormal habit of self-fertilisation, which in all probability will ultimately lead to its total extinction. Hence it does not need the assistance of insects; and it has accordingly never developed or else got rid of the bright outer ray-florets which may once have attracted them. Its tiny bell-shaped blossoms still retain their dwarf yellow corollas; but they are almost hidden by the green cup-like investment of the flower-head, and they are not conspicuous enough to arrest the attention of the passing flies. Here, then, we have an example of a plant just beginning to start on the retrograde path already traversed by the plantain and the spurges. If we could meet prophetically with a groundsel of some remote future century, I have little doubt we should find its bell-shaped petals as completely degraded as those of the plantain in our own day. The general principle which these cases illustrate is that when flowers have always been fertilised by the wind, they never have brilliant corollas; when they acquire the habit of impregnating their kind by the intervention of insects, they almost always acquire at the same time alluring colours, perfumes, and honey; and when they have once been so impregnated, and then revert once more to wind-fertilisation, or become self-fertilisers, they generally retain some symptoms of their earlier habits, in the presence of dwarfed and useless petals, sometimes green, or if not green at least devoid of their former attractive colouring. Thus every plant bears upon its very face the history of its whole previous development. XV. _BUTTERFLY PSYCHOLOGY._