Some authors have maintained that the amount of variation in our domestic productions is soon reached, and can never afterward be exceeded.

It would be somewhat rash to assert that the limit has been attained in any one case; for almost all our animals and plants have been greatly improved in many ways within a recent period; and this implies variation.

It would be equally rash to assert that characters now increased to their utmost limit, could not, after remaining fixed for many centuries, again vary under new conditions of life.

No doubt, as Mr. Wallace has remarked with much truth, a limit will be at last reached.