294 The Descent of Man. Past II. 



Order, Cohcrptera (Beetles). — Many beetles are coloured so as 

 to resemble the surfaces which they habitually frequent, and 

 they thus escape detection by their enemies. Other species, for 

 instance diamond-beetles, are ornamented with splendid colours, 

 which are often arranged in stripes, spots, crosses, and other 

 elegant patterns. Such colours can hardly serve directly as a 

 protection, except in the case of certain flower-feeding species ; 

 but they may serve as a warning or means of recognition, on the 

 same principle as the phosphorescence of the glow-worm. As 

 with beetles the colours of the two sexes are generally alike, we 

 have no evidence tlat they have been gained through sexual 

 selection ; but this is at least possible, for they may have been 

 developed in one sex and then transferred to the other ; and 

 this view is even in some degree probable in those groups which 

 possess other well-marked secondary sexual characters. Blind 

 beetles, which cannot of course behold each other's beauty, 

 never, as I hear from Mr. Waterhouse, jun., exhibit bright 

 colours, though they often have polished coats ; but the expla- 

 nation of their obscurity may be that they generally inhabit 

 caves and other obscure stations. 



Some Longicorns, especially certain Prionidse, offer an excej 

 tion to the rule that the sexes of beetles do not differ in colour. 

 Most of these insects are large and splendidly coloured. The 

 males in the genus Pyrodes,"' which I saw in Mr. Bates's col- 

 lection, are generally redder but rather duller than the females, 

 the latter being coloured of a more or less splendid golden-green. 

 On the other hand, in one species the male is golden-green, the 

 female being richly tinted with red and purple. In the genus 

 Esmeralda the sexes differ so greatly in colour that they have 

 been ranked as distinct species ; in one species both are of a 

 beautiful shining green, but the male has a red thorax. On the 

 whole, as far as I could judge, the females of those Prionidas, in 



"^ Pyrodes pukherrinms, in the family of Longicorns. Messrs. 



which the sexes differ conspicuously, R. Trimen and Waterhouse, jun., 



has been described by Mr. Bates in inform me of two Lamellicorns, 



' Transact. Ent. Soc' 1869, p. 60. viz., a Peritrichia and Trichius, the 



I will specify the few other cases in male of the latter being more 



which I have heard of a difference obscurely coloured than the female, 



m colour between the sexes of In TiUus elongatus the male is black, 



beetles. Kirby and Spence (' In- and the female always, as it is 



troduct. to Entomology,' vol. ill. p. believed, of a dark blue colour, with 



301) mention a Cautharis, Meloe, a red thorax. The male, also, of 



Rhagium, and the Leptura testacea ; Orsodacna atra, as I hear from Mr. 



the male of the latter being tes- Walsh, is black, the female (the 



taceous, with a black thorax, and so-called 0. ruficoUis) havJDg a 



the female of a. dull red all over, rufous thorax. 

 These two latter beetles belong to 



