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APPENDIX 
yet uncertain whether it is in a state of evolution or retrogression, must 
eventually either be perfected or disappear. 
Comparing the scent-organs of Antirrhaea archaea with those of 
Epicalia acontius, which I have previously described, we find an almost 
complete agreement between their component parts. In both species 
those margins of the wing which overlap each other, are considerably 
dilated and arched in the male sex : in both the under side of the upper 
wing is furnished with a mane of long hair inserted along the internal 
[submedian] nervure, and covering a scent-patch, well developed in the 
Epicalia , rudimentary in Antirrhaea. Opposite the mane, there is in both 
species on the upper surface of the lower wing, a scent-patch, whose 
central part occupies the angle between the two branches of the subcostal 
nervure, extending from thence into the three adjoining areas of the wing. 
Now all this would be very simple, and would be easily explained if the two 
species belonged to the same, or to allied genera, for then all the characters 
in which their scent-organs correspond might have been derived from a 
common ancestor. So far from this being the case, however, they are of 
two very different sub-families, Antirrhaea being claimed by the Satyridae 
and Epicalia by the Nijmphalidae , while even the nearest relatives of both 
are destitute of similar organs. They are completely wanting, for instance, 
in Epicalia numilia. Hence, there can be no doubt that the scent-organs 
have been independently developed in these two species, and that every¬ 
thing they have in common is solely due to the circumstance that they 
are adapted to fulfil the same function. The two organs are not 
“ homologous,” but simply “ analogous,” and they furnish a most notable 
example of “ convergence,” to use the modern term for a resemblance 
caused, not by inheritance, but by adaptation to similar circumstances. 
I know of no other case which proves so clearly and irrefragibly, and 
attests with such force, the truth of a principle which should never be lost 
sight of in morphological studies, viz.—when in two species certain 
organs which serve the same function, are found in the same place, are 
composed of the same parts occupying the same relative positions, and 
exhibiting similar forms—all this by itself constitutes no sufficient proof 
that these organs are homologous, nor does it give ground for placing the 
two species in the same family. 
