The first is the handsome Papilio memnon, a splendid butterfly of a deep black colour, dotted over with lines and groups of scales of a clear ashy blue. Its wings are five inches in expanse, and the hind wings are rounded, with scalloped edges. This applies to the males; but the females are very different, and vary so much that they were once supposed to form several distinct species. They may be divided into two groups--those which resemble the male in shape, and, those which differ entirely from him in the outline of the wings. The first vary much in colour, being often nearly white with dusky yellow and red markings, but such differences often occur in butterflies. The second group are much more extraordinary, and would never be supposed to be the same insect, since the hind wings are lengthened out into large spoon-shaped tails, no rudiment of which is ever to be perceived in the males or in the ordinary form of females. These tailed females are never of the dark and blue-glossed tints which prevail in the male and often occur in the females of the same form, but are invariably ornamented with stripes and patches of white or buff, occupying the larger part of the surface of the hind wings. This peculiarity of colouring led me to discover that this extraordinary female closely resembles (when flying) another butterfly of the same genus but of a different group (Papilio coön), and that we have here a case of mimicry similar to those so well illustrated and explained by Mr. Bates.[ Trans. Linn. Soc. vol. xviii. p. 495; "Naturalist on the Amazons," vol. i. p. 290.]
That the resemblance is not accidental is sufficiently proved by the fact, that in the North of India, where Papilio coön is replaced by an allied form, (Papilio Doubledayi) having red spots in place of yellow, a closely-allied species or variety of Papilio memnon (P. androgeus) has the tailed female also red spotted. The use and reason of this resemblance appears to be that the butterflies imitated belong to a section of the genus Papilio which from some cause or other are not attacked by birds, and by so closely resembling these in form and colour the female of Memnon and its ally, also escape persecution. Two other species of this same section (Papilio antiphus and Papilio polyphontes) are so closely imitated by two female forms of Papilio theseus (which comes in the same section with Memnon), that they completely deceived the Dutch entomologist De Haan, and he accordingly classed them as the same species!