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372 TROPICAL NATUREghost-moth may render it more easily seen by the femalewhile flying about in the dusk ;and if to this we add that itwill be also more readily distinguished from allied species, wehave a reason for diverse ornamentation in these insects quitesufficient to account for most of the facts, without believingin the selection of brilliant males by the females, for whichthere is not a particleof evidence. 1Probable use of the Horns of BeetlesA somewhat analogous case is furnished by the immensehorns of some beetles of the families Copridae and Dynastidse,which Mr. Darwin admits are not used for fighting, and thereforeconcludes are ornaments, developed through selection ofthe larger -horned males by the females. But it has beenoverlooked that these horns may be protective. The malesprobably fly about most, as is usually the case with maleinsects ;and as they generally fly at dusk they are subject tothe attacks of large-mouthed goatsuckers and podargi, as wellas of insect -eating owls. Now the long, pointed, or forkedhorns, often divergent, or movable with the head, wouldrender it very difficult for these birds to swallow such insects,and would therefore be an efficient protection, just as are thehooked spines of some stingless ants and the excessively hardinteguments of many beetles, against the smaller insectivorousbirds.Cause of the greater Brilliancy of some Female InsectsThe facts given by Mr. Darwin to show that butterfliesand other insects can distinguish colours and are attracted bycolours similar to their own, are quite consistent with theview that colour, which continually tends to appear, is utilisedfor purposes of identification and distinction when not requiredto be modified or suppressed for the purpose of protection.The cases of the females of some species of Thecla, Callidryas,Colias, and Hipparchia, which have more conspicuous markingsthan the male, may be due to several causes : to obtaingreater distinction from other species ;for protection frombirds, as in the case of the yellow-underwing moths; whilesometimes as in Hipparchia the lower intensity of colour-1 See M. Fabre's testimony on this point, Descent of Man, p. 291.