( 616 ) 
§ II. On the Sexual Spots of the Males of Danais erippus 
and D. gilippus. 1 
Plate A, 
In the account which he gives of the generic characters of Danais , 
Doubleday 2 makes the following statement as to the sexual differences 
which are found on the wings of these butterflies :— 
The males of the first group (containing the African species now 
included in the genus Amauris 3 ) “ have a patch of peculiarly formed and 
closely placed scales situated on the submedian nervure of the posterior 
wings, not far from the anal angle.” In the second group (to which belong 
all the American species) the “ sexual spot ” is found on the first branch of 
the median nervure. In the third group the sexual spot is placed either on 
the same branch or on the submedian nervure, and is in the form of a 
perfect pocket, opening on to the upper surface of the wing, at the bottom 
of which, at least in dried specimens, a little dark powder is found. In 
the species of the fourth group (now forming the genus Ideopsis 4 ) the sexual 
patch is absent from the hind-wings. 
Decent discoveries 5 show that the sexual marks which characterize the 
wings of many male butterflies are scent-organs, and they exhale at times 
a distinct odour, which is undoubtedly agreeable to the females of the 
respective species. I therefore proceeded to examine the sexual spots of 
our two species of Danais (Danais erijppus , Cram, and D. gilippus , Cram.) 
and found in them a most interesting structure, which appears to me 
worthy of detailed description. The “ sexual spot ” (I provisionally retain 
Doubleday’s name for the structure until its functions are definitely 
ascertained) is placed, in our D. erippus and D. gilippus , on the hind-wings, 
between the submedian nervure and the first branch of the median, being 
only separated from the latter by a very narrow interval, which in D. erippus 
barely equals, and in D. gilippus scarcely exceeds, the diameter of the branch 
itself (PL A, Figs. 1, 2, 7, 8). It is visible on both sides of the wing, 
forming a small black swelling more prominent on the upper surface. The 
1 Archives do Museu National do Rio de Janeiro , II. (1877), pp. 25-29. By Dr. 
Fritz Muller, Travelling Naturalist for the National Museum. 
2 Doubleday, Westwood, and Hewitson, Genera of Diurnal Lepidoptera, 
p. 89.—F.M. 
3 Kirby, A Synonymic Catalogue of Diurnal Lepidoptera, 1871, p. 8.—F.M. 
4 Kirby, loc. tit., p. 2.—F.M. 
5 Fritz Muller, Kosmos, I., 1877, p. 391 [see § X., p. 655].—F.M. 
