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§ IV. On Scent-organs on the Legs of certain Lepidoptera . 1 
Plate C. 
Darwin, speaking of sexual selection, and the secondary sexual cha¬ 
racters of insects, makes the following statement:— 
“The sexes of many species in all the orders present differences, of 
which the meaning is not understood. . . . They abound in the Lepido¬ 
ptera : one of the most extraordinary is that certain male butterflies have 
their fore-legs more or less atrophied. . . . The wings, also, in the two 
sexes often differ in neuration, and sometimes considerably in outline, as 
in the Aricoris epitus. . . . The males of certain South American butter¬ 
flies have tufts of hair on the margins of the wings, and horny excrescences 
on the discs of the posterior pair. In several British butterflies, as shown 
by Mr. Wonfor, the males alone are in parts clothed with peculiar scales.” 2 
Almost all these sexual differences in the Lepidoptera—completely 
inexplicable only a few years ago—have now become clear and intelligible 
since the discovery has been made that they are directly or indirectly 
concerned with the production or diffusion of a peculiar scent which must 
certainly be agreeable to the females. Foremost in this category are, 
first, the tufts or manes which are frequently found on the anterior margin 
of the hind-wings, and produce a scent which is strongest in Gallidryas 
cipris , but very perceptible and very agreeable in Dircenna xantho \Itho- 
miinae ], and in other species ; secondly, the “ specialized scales ” of very 
varied forms, which exist on the wings of the males of many species of 
Satyrinae , Heliconinae , Nymphalinae , Pierinae , etc., to which Bernard 
Deschamps 3 gave the name of “ plumules ” ; thirdly, the “ horny excre¬ 
scences ” or “ sexual spots ” which are seen on the disc of the hind-wings 
of Danais erippus , and gilippus . 4 
As to the sexual difference in the disposition of the wing venation, this 
also, in most, if not in all cases, owes its existence to the male scent-organs, 
which in some way displace certain nervures ; as may be easily verified in 
the genera Dircenna , Mechanitis , Thecla {e.g. T. acmori), among diurnal, 
1 Archivos do Museu Nacional do Rio de Janeiro , II. (1877), pp. 87-42. By Dr. 
Fritz Miiller, Travelling Naturalist for the National Museum. 
2 Descent of Man, 2nd Edition, 1874, pp. 276, 277.—E.B.P. 
3 Annales des Sc. Nat. 1835, III., p. 120. Quoted by Chenu, Encyclop. d'Uist. 
Nat. Pavilions, I., p. 8.—F.M. 
4 In the Jen. Zeitschr., XI. (1877) [viz. § I of this Appendix], is published 
a resume of what our authors have written, which may be consulted as to scent- 
organs on the wings of butterflies, and is the first attempt to demonstrate the 
functions of these organs.—F.M. 
