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120 an expedition was made up the Chipari, a branch river which enters the Tapajos about eight miles above it. At this time Bates was thrown in contact with the Mundurucus Indians, and was able to acquire much valuable ethnological information. It was also during this second jonrney that the long stay was made at Ega, and the many excursions in its neighborhood resulted in so much general knowledge, both zoölogical and geographical. Bates returned again to Pará on the 17th of March, 1859, after an interval of seven and a half years in the interior. During this long sojourn in the tropics Mr. Bates obtained more than 14,700 species of animals, of which 14,000 were insects, and of these 8,000 were new to science.

After they had been two years together in South America, Mr. Wallace separated from Bates, to visit the Rio Negro and the upper waters of the Orinoco, whence he subsequently went to the Malay Archipelago.

Mr. Bates sent contributions to The Zoölogist from time to time during the whole of the eleven years which he spent in the Amazonian regions. One of his letters gives a curious picture of him as equipped for a day's expedition, in colored shirt, trousers, boots, and old hat; his double-barreled gun over his shoulder, loaded with two kinds of shot; his net in his right hand, while "on my left side is suspended a leathern bag with two pouches, one for my insect-box, the other for powder and two sorts of shot; on my right side hangs my 'game-bag,' an ornamental affair, with red leather trappings and things to hang lizards, snakes, frogs, or large birds; one small pocket in this bag contains my caps, another papers for wrapping up the delicate birds; others for wads, cotton, box of powdered plaister, and a box with damped cork for the micro-lepidoptera; to my shirt is pinned my pincushion, with six sizes of pins."

The summary of the adventures and results of his voyage is given in the Naturalist on the Amazons, "one of the most delightful books of travel ever perused, full of varied information charmingly arrayed," which, prepared after the persistent urgency of Darwin, was published in 1863. This was Mr. Bates's only book.

His most memorable contribution to biological science was a paper published in the Transactions of the Linnrean Society, entitled Contributions to an Insect Fauna of the Amazon Valley, in which the phenomenon of mimicry was unfolded and explained as a means of protecting animals—by giving them guises tending to ward off pursuit by enemies, or by so likening them to surrounding objects that they escape notice. Darwin spoke of the book as one of the most remarkable that he ever read, and "as clearly stating and solving a wonderful problem," and found in it a strong support of his theory of natural selection.