Within a few weeks of the hundredth anniversary of Darwin’s birth, and nearly midway between the fiftieth anniversaries of the publication of Natural Selection on July 1 last and the Origin of Species on Nov. 24 next, it seemed to me specially appropriate to select for this address a subject that is closely associated with Darwinian teachings. Although he did not publish it during his lifetime, we now know from his correspondence that Darwin independently originated the interpretation of Mimicry which was afterwards suggested by H. W. Bates. Its development in the mind of the naturalist of the amazons and the rival theory afterwards suggested by Fritz Müller were both of them the direct outcome, in Bates’s case the very speedy outcome, of the Origin. The deep interest which Darwin took in the hypotheses of both naturalists is proved by many a letter in his published correspondence. All this forms a peculiarly fascinating chapter of ancient history, – nevertheless ancient history; but if we desire to choose a subject because of the light it can throw today and is certain to throw tomorrow upon evolution and its causes, there is no study which for promise as well as performance can be set on a higher level than Mimicry.