[22] Cf. Poulton, _Darwin and the 'Origin,'_ 1909, pp. 177-186. [23] The N. American members of this genus are often referred to as _Basilarchia_. [24] _Darwinism_, 1890 (1st Edition 1889), p. 264. [25] _Macrolepidoptera of the World._ _Fauna Americana_, p. 98. [26] _Essays on Evolution_, 1908, p. 381. [27] These "unpalatable" butterflies are sometimes extensively preyed upon by insectivorous birds, when they fall an easier prey owing to their slowness (cf. p. 112). [28] See Shelford, PROC. ZOOL. SOC. 1902, p. 260. A coloured figure of both species is given in the paper. [29] _Macrolepidoptera of the World._ _Fauna Americana_, pp. 98-104, Plates 28-30. [30] "In what way our _Leptalis_ (= _Dismorphia_) originally acquired the general form and colour of Ithomiae I must leave undiscovered." _Trans. Linn. Soc._ vol. 23, 1862, p. 513. [31] _Darwinism_, 1890, pp. 242-244. [32] _Origin of Species_, 6th Edition, 1891, p. 354. [33] _H. misippus_ was at one time regarded as a clear case of Batesian mimicry. But in view of its plentifulness, of the fact that it may be abundant outside the area inhabited by its model, and of the ease with which it can establish itself in parts remote from its original habitat, _e.g._ S. America, it has come to be regarded by certain supporters of the mimicry theory as a Müllerian mimic. Cf. Poulton, _Essays on Evolution_, 1908, pp. 215-217. [34] An English translation of Müller's paper is given by Meldola, _Proc. Ent. Soc._, 1879, p. xx. [35] _Trans. Ent. Soc. Lond._, 1908, p. 93. [36] Provided of course that the type form remains in the majority. If the variation occurred simultaneously in more than 50% of A the advantage would naturally be with the variation. [37] It is possible to imagine an exceptional case though most unlikely that it would occur. Suppose for example that there were a number of distasteful species, say 20, all of different patterns, and suppose that in all of them a particular variation occurred simultaneously; then if the total shewing that variation from among the 20 species were greater than the number of any one of the species, all of the 20 species would come to take on the form of the new variation. In this way it is imaginable that the new pattern would gradually engulf all the old ones. [38] _Trans. Linn. Soc._ vol. 24, 1866. [39] These darker ribs are also present in the male and M female but are obscured owing to the generally deeper colour. [40] See Appendix II, p. 158. [41] _Spolia Zeylanica_, 1910. [42] We shall take it for the present that, from the point of view of mimicry, birds are the main enemies of butterflies (cf. Chap. IX). [43] See later, p. 119. [44] The specimens figured on Pl. V were dried in papers when taken. The body is consequently much compressed and the characteristic scarlet of _P. hector_ and _P. aristolochiae_ is largely hidden. [45] _Philosophical Transactions of the Royal Society_, vol. 204, 1913.