Two of such groups occur to me at once, in entomology, in Heliconiidæ and Erotylidæ of South America; the latter I think more interesting than the former for one reason--the species are more local, having feebler means of locomotion than the Heliconiidæ....--Yours very truly, HENRY WALTER BATES. * * * * * TO H.W. BATES _Amboyna. January 4, 1858._ My dear Bates,--My delay of six months in answering your very interesting and most acceptable letter dated an ideal absurdity put forth when such a simple hypothesis will explain _all the facts_. I have been much gratified by a letter from Darwin, in which he says that he agrees with "almost every word" of my paper. He is now preparing for publication his great work on species and varieties, for which he has been collecting information twenty years. He may save me the trouble of writing the second part of my hypothesis by proving that there is no difference in nature between the origin of species and varieties, or he may give me trouble by arriving at another conclusion, but at all events his facts will be given for me to work upon. Your collections and my own will furnish most valuable material to illustrate and prove the universal applicability of the hypothesis. The connection between the succession of affinities and the geographical distribution of a group, worked out species by species, has never yet been shown as we shall be able to show it. In this Archipelago there are two distinct faunas rigidly circumscribed, which differ as much as those of South America and Africa, and more than those of Europe and North America: yet there is nothing on the map or on the face of the islands to mark their limits. The boundary line often passes between islands closer than others in the same group. I believe the western part to be a separated portion of continental Asia, the eastern the fragmentary prolongation of a former Pacific continent. In mammalia and birds the distinction is marked by genera, families, and even orders confined to one region; in _insects_ by a number of genera and little groups of peculiar species, the _families_ of insects having generally a universal distribution. * * * * * _Ternate, January 25, 1858._