April z. 1879] 



NATURE 



503 



conclude, either that there is not a community of taste in 

 colour between insects and birds, or, that what may be 

 termed the normal colours of both have been more or 

 less intensified and utilised by natural selection in order 

 to attract insects and birds respectively. 



The next chapter, on the colour-sense in vertebrates, 

 clearly establishes the fact of the possession of this sense 

 by all vertebrate animals, but more especially by birds 

 and reptiles. The evidence of such a sense in mam- 

 malia generally is very scanty, though it undoubtedly 

 exists in monkeys ; while there are good reasons for be- 

 lieving that it is more acute in birds than even in our- 

 selves. Birds on the whole need to perceive colour more 

 than any other animals, both because the insects and 

 fruits and buds on which so many of them feed are small 

 variously-coloured objects, and because from their habits 

 they require to see and recognise these objects from a 

 considerable distance. It is therefore a remarkable con- 

 firmation of the modern theory — that the cones of the re- 

 tina are colour organs while the rods are only light 

 organs, that in birds the cones are three times as numerous 

 as the rods, while in mammals they are less numerous. 

 Nocturnal birds, such as owls, however, have very few 

 cones, while nocturnal mammals have none. The macula 

 lutea, a central yellow spot consisting largely of cones, is 

 found in man and monkeys only, while it exists in all 

 diurnal birds, and these in addition have their cones fur- 

 nished with variously-coloured globules, which are sup- 

 posed to give a still more perfect perception of colour. 

 The eye of the chameleon is as perfect as that of a bird, 

 and this accords with its capacity of colour change, and 

 the extreme accuracy with which it detects and captures 

 insects. Mammals, on the other hand, even the insec- 

 tivorous and frugivorous kinds, have very little occasion 

 for a refined colour sense, since the great mass of creeping 

 insects are of obscure colours, while the squirrels and 

 allies feed on brown nuts rather than on coloured fruits. 

 The evidence seems to show, therefore, that a tolerably 

 perfect colour-sense has only been attained, among mam- 

 malia, in the monkeys and man, while even in these it is 

 probably very inferior to that of birds. It seems probable, 

 therefore, that the prevalence of colour-blindness is really 

 an indication of the colour sense in man having been a 

 comparatively recent development, instead of being, as 

 Mr. Allen thinks, a disease of civilisation. An acute colour 

 sense is certainly not of the first importance to savages; and 

 though our author has adduced valuable evidence that 

 most savages distinguish colours just as well as we do, it 

 is very important to ascertain whether colour-blindness 

 exists among uncivilised peoples to a greater or a le.ss ex- 

 tent than among Europeans. 



The next chapter, on the direct action of the colour 

 sense upon the animal integuments, deals with the theory 

 of sexual selection as advanced by Mr Darwin, and 

 endeavours to support it by a variety of general considera- 

 tions. Many of these arguments are very weak, and are 

 often founded on insufficient or erroneous facts, some of 

 which I shall endeavour to point out. The great aim of 

 this chapter is to prove that the colours of animals are 

 I intimately associated with the colours of the objects they 

 I feed upon. Butterflies and moths being the most beauti- 

 hilly coloured of all insects and feeding on flowers, is 

 held to be the first great fact in support of this view ; and 



this is backed up by the remark that "the colours of 

 caterpillars are mostly protective, being due to natural 

 selection alone, while those of butterflies are mostly 

 attractive, being largely due to sexual selection." To 

 this we must altogether demur, as slurring over what is 

 really a stupendous difficulty in the way of the theory. 

 So far from the colours of caterpillars being "mostly 

 protective" every entomologist knows that a large num- 

 ber of caterpillars in every part of the world are con- 

 spicuously coloured, and what is more to the point that 

 their colours are as brilliant and varied as those of butter- 

 flies themselves, if we take into account the nature of 

 their integument, the small amount of surface, and the 

 uniform cylindrical form of their bodies. The caterpillar 

 of Papilio dissimilis, for instance, on a bluish green 

 ground has a series of broad irregular longitudinal bands 

 of the richest orange yellow, and between these there are 

 a number of round red spots ; while those of many of the 

 Euplaeas are adorned with exquisite pink and yellow 

 markings, and with a nimiber of long fleshy processes of 

 equally brilliant colours. Owing to caterpillars being so 

 difficult to preserve, and being rarely collected and 

 figured in their native countries, comparatively few of 

 them are known, but it is certain that they often exhibit 

 the most brilliant hues and the most exquisite patterns ; 

 and as they may be said to feed invariably on green 

 leaves, while sexual selection cannot afiect them, the 

 natural inference is that the same general laws which 

 produce colour in them are quite sufficient for the pro- 

 duction of even more varied hues in the perfect insects, 

 whose expanded wing surfaces, ever varying in size, form, 

 and neuration, offer a field so much better fitted for its 

 development. 



In beetles the appearance of colour is also attempted to 

 be correlated with their flower-haunting habits by means 

 of equally doubtful facts. The magnificent Buprestidas 

 and Longicorns are, as far as my experience goes, almost 

 wholly wood-feeders, frequenting the bark of dead trees, 

 and very rarely found on flowers ; the Cleridae and 

 Silphidae feeding on dead animal matter, are often bril- 

 liantly coloured ; and generally in beetles, the absence of 

 coloiur may be traced to the need of concealment and 

 protection, whUe whenever a special mode of protection 

 exists, whether by nauseous secretions, hard integuments, 

 rapid flight, or facilities for concealment, then colour 

 appears in infinitely various phases ; and this law gener- 

 ally prevails throughout the whole insect-world. In his 

 argument in favour of bright hues being attractive to the 

 opposite sexes of insects, Mr. Allen seems always to 

 forget that it is the male that is attracted to the female, and 

 not vice versd; and when he says (p. 158) that he "can- 

 not see why Mr. Wallace, who allows the attractive nature 

 of colouring in flowers, should deny its attractive nature 

 in the question of sex," I reply, that in flowers colour 

 enables the insect to recognise the species, but no one 

 has ever asserted that insects improve and alter the 

 colour of flowers by their preference for certain varieties 

 of colour irrespective of the honey or pollen produced j 

 and in like manner I maintain that the colour of an insect 

 is a guide to easy recognition by its mate, but that there 

 is not one single particle of evidence to show that minute 

 differences in the colour of the same species are observed 

 by insects, still less that such differences are so important 



