To prove the correctness of the hypothesis of an actual process of selection--which we assume in our interpretation of mimicry--I mean the assumption that the disguise of the species seeking protection really deceives the enemy, and thus actually affords protection, I need only cite the evidence of an acute and experienced entomologist who was himself deceived by it. Seitz[6], to whom we owe many valuable biological observations on butterflies, relates that, while he was collecting in the neighbourhood of the town of Bahia, he was surrounded by swarms of _Catopsiliæ_, similar to our lemon butterfly, especially the common _Catopsilia argante_, but he took no notice of these, as he 'had already collected as many of them as he wanted.' It was only when he saw a pair _in copula_ that he caught them in his net. But to his extreme surprise he found that he had not caught a _Catopsilia_, but a butterfly of the family Nymphalidæ, one of those _Anææ_ whose numerous species are distributed over South America. These _Anææ_ are dark, or beautifully bright on the upper surface, but on the under side are leaf-coloured, and one of them bears the name _Anæa opalina_, because it is quite clear and pale, and of opal-like brilliance. The captive was nearly related to this species. Seitz was so much surprised by the discovery that the male, which had quickly detached itself from the female, escaped him, and he could only make out that, 'as it flew away, it unfolded dark wings, which certainly bore little resemblance to those of the lemon butterfly.' In the hope of securing more of this rare booty he then hunted only for _Catopsilia argante_, without however securing another coveted specimen--he caught no more _Anœæ_, which shows that in this case, too, the mimetic species was much rarer. [6] In citing this observation of Seitz, I do not mean to assert that there is true mimicry between _Anæa opalina_, or its allied species in Bahia, and the _Catopsilia_, though I regard this as extremely probable, because of the marked dimorphism between the male and the female, in conjunction with the very striking resemblance of the female to the _Catopsilia_. The example was given only to show how very deceptive such resemblances may be. To assert with confidence that it is a case of mimicry we should require to know that _Catopsilia_ is immune, and on that point we have as yet no information. PLATE II FIG. 12-15 REPRESENT A 'MIMICRY-RING' COMPOSED OF FOUR IMMUNE SPECIES BELONGING TO THREE DIFFERENT FAMILIES AND FOUR DIFFERENT GENERA. 12. HELICONIUS EUCRATE, BAHIA. 13. LYCOREA HALIA, BAHIA. 14. MECHANITIS LYSIMNIA, BAHIA. 15. MELINÆA ETHRA, BAHIA. 16, 17. PERHYBRIS PYRRHA, MALE AND FEMALE, S. AMERICAN 'WHITES' (PIERIDÆ). THE FEMALE MIMICS AN IMMUNE HELICONIID, WHILE THE MALE SHOWS ONLY AN INDICATION OF THE MIMETIC COLOURING ON THE UNDER SURFACE.