[page] i

[page] ii

Prof. Westwood exhibited two females of Anthocharis Cardamines, each of which had a dash of the orange-colour of the male on one of its fore wings; also a female of Polyommatus Adonis, the left fore wing of which was dashed with blue like the male; also a male of Siderone Isidora, one side of which was partially coloured like the female.

The President suggested that the existence of specimens of this kind might be explained on Mr. Darwin's theory of sexual differences. The hypothesis was that the sexes of a species, though now differently coloured, were once alike; the divergence from the original type was sometimes in one sex, and in one direction only; at other times in both sexes, and in opposite directions; and it might be that these curious cases of the union of opposite sexual colours were only instances of a partial reversion, or modifications of reversion, to the original ancestral type.