i. In some species the sexes are either partly or wholly of a

different _colour_. Thus, in the order _Coleoptera_, the elytra of the male of _Rhagium meridianum_ F. are testaceous, and those of the female black. _Leptura rubra_ of Linné, with red elytra, is the female of his _L. testacea_, in which they are testaceous. _Cantharis dermestoides_ of the same author is the other sex of his _Meloe Marci_; one of which is chiefly testaceous, and the other black: which seems to have so misled Linné, that he placed them in different genera. One more instance in this order, the female of _Cicindela campestris_, as was first observed to me by our friend Sheppard, has a black dot on each elytrum, not far from its base near the suture, which the male has not.

Amongst the _Orthoptera_, the male _Locustæ_ F., as Professor Lichtenstein has informed us[706], have a fenestrated ocellus, which is not to be found in the other sex. I was once attending to the proceedings of a Hemipterous species, _Pentatoma oleracea_ Latr., which I found in union: the paired insects had white spots, but another individual was standing by them, in which the spots were of a sanguine hue. I mention this by the way only--the spots in the prolific sexes being of the same colour: but might not the red spotted one be a neuter?

The sexes of many _Lepidoptera_ likewise differ in their colour. I must single out a few from a great number of instances. The males of _Lycæna Argus_ F. have the upper surface of their anterior wings of a dark blue, while in the female it is wholly brown. The wings of the former sex of _Hypogymna dispar_ are gray, clouded with brown; but those of the latter are white, with black spots. In the brimstone butterfly (_Colias Rhamni_), which is one of the first that appear in the spring, the wings of the male are yellow--of the female whitish. In the common orange-tip (_Pieris Cardamines_ F.), one sex has not the orange tip to the upper wings: and, to name no more, the male of _Lycæna dispar_, one of our rarest and most beautiful butterflies, has only a single black spot in the disk of its fulgid wings; while in the other sex, the primary pair have nine, and the secondary are black, with a transverse orange fascia near the posterior margin. But the most remarkable difference in this respect observable in the insects of the order in question, takes place in a tribe, of which only one species is certainly known to inhabit Britain--I mean the _Papiliones Equites_ of Linné: what he has called his _Trojani_ and _Achivi_ in some instances have proved only different sexes of the same species. Mr. MacLeay's rich cabinet affords a singular instance confirming this assertion;--a specimen of a Papilio is divided longitudinally, the right hand side being male, and the left hand female. The former belongs to _P. Polycaon_, a Grecian, the latter to _P. Laodocus_, a Trojan. An instance of two _Grecians_ thus united is recorded in the _Encyclopédie Méthodique_, as exhibited in a specimen preserved in the Museum of Natural History at Paris; which on the right hand side is _P. Ulysses_, on the left _P. Diomedes_[707].

In the _Neuroptera_, the _Libellulidæ_ are remarkable for the differences of colour in the sexes. In the common _Libellula depressa_, which you may see hawking over every pool, the abdomen of the male is usually slate-colour, while that of his partner is yellow, but with darker side-spots. Reaumur, however, noticed some males that were of the same colour with the females[708]. Schelver observed, when he put the skins of _Libellula depressa_ into water, that the colours common to both sexes were in the substance of the skin, and remained fixed; while those that were peculiar to one could be taken off with a hair-pencil, and coloured the water: which therefore were superficial, and, as it were, laid on[709]. The yellow males, therefore, that Reaumur observed, were probably such as had the superficial blue colour which distinguishes them washed off. In _Calepteryx Virgo_ Leach, the former are of a lovely silky blue, and the latter green. In _Agrions_ F. nature sports infinitely in the colours of the sexes.

In the order _Hymenoptera_ there are often differences equally great; the sexes of many of the Ichneumons and Saw-flies are of quite different colours. The former tribe Linné has divided into sections, from the white annulus observable in the antennæ of some, and from the colour of their scutellum: but these are often merely sexual characters[710]. The male of _Anthophora retusa_ Latr., a kind of wild bee, is wholly black, the female wholly gray, and of so very different an aspect that they were long regarded as distinct species; a mistake which has likewise occurred with regard to the sexes of _Osmia cærulescens_, another bee, of which the male has a bronzed and the female a violet abdomen[711]. The nose of male _Andrenæ_ Latr. is often yellow, or white, as in _A. hæmorrhoidalis_--when that of the female is black[712]. The _labrum_ also is often of a different colour in the sexes, as in _Ceratina_ Latr.

In the _Diptera_, _Aptera_, _Arachnida_, &c., I am not aware of any striking difference in the colours of the sexes.