American region, notwithstanding that the districts Abound with insectivorous birds. Now, Mr. Bates has observed that where large numbers of this family are found they are always accompanied by species of a totally distinct family which closely resemble them in size, form, color, and markings. So close is the resemblance that Mr. Bates often found it impossible to distinguish members of one family from those of the other when the insects were on the wing; and he observed, moreover, that when a local variety of a species of the _Heliconidae_ occurred, there was found also a butterfly of another family imitating that local variety. There is no difficulty at all in distinguishing the imitators from the imitated, for the latter have all a family likeness, while the former depart from the normal form and likeness of the families to which they respectively belong. What is the meaning of this curious fact? It is this: the _Heliconidae_, or imitated butterflies, are not persecuted by birds, dragon-flies, lizards, or other insectivorous enemies, while the members of the imitating families are subject to much persecution. The butterflies imitated are said to owe their immunity from persecution to their offensive odor, while no such fortunate character belongs to the imitating insects. But how, we naturally ask, has this change of color and form been effected? Mr. Darwin and Mr. Bates explain it on the principle of natural selection. Let us suppose that a member of the persecuted family gave birth to a variety--and there is a tendency in all animals to produce varieties--exhibiting a very slight resemblance to some species of _Heliconidae_. This individual, in consequence of this slight resemblance, would have a better chance of living and producing young than those of its relatives which bear no resemblance whatever to the unmolested family. Some of the offspring of this slightly favored variety would very probably show more marked resemblance to the unpersecuted butterflies; and thus the likeness between insects of totally distinct groups would in course of time be, according to the law of inheritance, quite complete. This is the explanation which Mr. Bates gives of this natural phenomenon. The phenomenon itself is an undoubted one; whether it is or is not satisfactorily accounted for, cannot at present be determined; we must wait for further investigation. We had intended to speak of some of the South American palms, those wondrous and valuable productions of tropical countries, the India-rubber trees, and other vegetable productions of the Amazons, but we must linger no longer with the excellent naturalist from whose volumes we have derived so much pleasure. Mr. Bates has written a book full of interest, with the spirit of a real lover of nature and with the pen of a philosopher. {191}