From H. W. Bates   20 April 1868

My dear Mr Darwin

I have found amongst my old papers a rude drawing of the conspicuous caterpillar which you intend to mention so enclose it.¹ I believe it is natural size; the black is not deep enough, otherwise I think the colour is accurate

The species of Æneas group of Papilio in which the sexes show no difference in colours or pattern are²

P. Ascanius in both sexes is handsome; I think more conspicuous & gay in colouring than any of the other four species here mentioned. The whole Æneas group is remarkable for its rich, strongly-constrated³ & conspicuous colouring; but the rule is—less richness of tint in ♀ than in ♂, although the ♀ has often more variety of colour. It is very clear there is no adaptation of female colouring to disguise in this group.

The females of Argynnis Diana & A. Sagana are of olive-brown or blackish colours relieved by lighter marks.⁴ Regarded absolutely one cannot consider them less beautiful than their males; but there is no doubt, here, adaptation for purposes of disguise has taken place; Entomologists of the countries where they are found alone could say what they imitate; I have no idea myself; but A. Sagana ♀ is coloured much like many common butterflies of Adolias group found in some countries.⁵

Yours sincerely | H W Bates

A capital suggestion that of H. Doubleday!⁶