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APPENDIX 
In the males of Colaenis \_Metamorpha ] dido the scales occur elsewhere 
than on the upper surface of the wings. I first observed their arrange¬ 
ment more accurately in Heliconius besckei (PL H, Fig. 2). The scales of 
the diurnal Lepidoptera form, as is well known, transverse rows, each one 
nearer the base of the wing covering the insertion of the succeeding row 
like slates on a roof. In each row two kinds of scales alternate, those 
resting on the membrane of the wing (lower scales) being broader and 
shorter, the others resting on them (covering scales) narrower and longer. 
Where, on the area already described, this regular arrangement is fully 
carried out, the scent-scales take the place of the covering scales; but 
their points of insertion rarely lie in the same line as those of the other 
scales, being usually nearer to the base of the wing. Where the arrange¬ 
ment of the scales is less regular—especially along the costal nervure, 
where the scent-scales are most numerous—these latter are also apparently 
scattered quite irregularly among the others. 
Their significance as scent-scales is indicated by—(1) their restriction 
to the male sex ; (2) their occurrence at that place, where above all 
others, the scent structures are found. Here, viz. on the part of the hind¬ 
wing covered by the posterior margin of the fore-wing, is found, among 
the Danaidae , the scent apparatus in species of Euploea , here the long 
hair-tufts of Ithomia, Mechanitis and most of the Heliconius- like Danaidae 
\_Ithomiinae~\ ; among the Satyridae , the large white scent-patch of 
Gnophodes morpena , the hair-tufts of various species of Mycalesis , a patch 
with long black silky hairs in Bia actorion ; among the Elymniinae , 
the hair-tufts of Elymnias ; among the Morplnnae , the oval leather-brown 
patch of Zeuxidia , and the tufts of Tenaris , Clerome and Thaumantis ; 
among the Brassolinae 1 the oval patch of Dasyophthalma ; among the 
Nymphalinae, the patch of Lachnoptera ; among the Pierinae , the scent- 
patch of several species of Leptalis , Gallidryas, Nathalis, etc.; among the 
Hesperidae, the tufts of Caecina ; finally among moths ( Hyponomeutidae ) 
the long light grey hair-tufts of Trichostibas. 
3rd. The fringes on the apical margin, which both favour the collection 
of the perfume when the wings are closed, and also its rapid evaporation, 
as soon as the wings are spread. 
4th. The socket in which the stalk is placed, exactly like those found 
in scent-patches diffusing a strong unmistakable scent. 
Of the genera usually placed near the Maracuja butterflies, I have 
only examined Acraea , Argynnis and Melitaea (of the latter both the 
Alpine species, collected by my brother Hermann Muller), but have been 
unable to discover on the wings anything similar to the scent-scales of 
Heliconius, Eueides, Colaenis and Dione. Thus even this inconspicuous 
character confirms once again the close affinity uniting the members of 
the Maracuja group and their isolation. 
Besides the scents which the male butterflies emit to make themselves 
acceptable to the female they are courting, many species produce odours 
