HARDWICKE'S SCIENCE-GOSSIP. 



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a benefit shared by all the species protected by 

 warning colouration. In many cases (Danais, 

 Heliconia, etc.) sexual colouring has been made 

 use of for warning! purposes. Among these genera 

 immense numbers of species closely resemble one 

 another, this being an instance in which natural 

 selection has arrested divergence in allied species 

 for the reasons given above. It is evident that 

 any species not possessing the unpleasant properties 

 in so great a degree will nevertheless benefit by 

 possessing the same or similar markings as its 

 nauseous congeners, while the latter will share the 

 advantage, by having their patterns more widely 

 advertised. This leads on to cases of true protective 

 mimicry, in which certain species not possessing 

 special protection nevertheless share the advantages 

 of those possessing it by imitating their patterns, and 

 thus trading on their reputation. Such species often 

 belong to widely different genera from those 

 mimicked, and the close resemblance to the latter 

 is therefore brought about by convergence of 

 character, rather than by arrested divergence. The 

 same remark applies to many of the cases of warning 

 colours which have independently arisen in distinct 

 genera. It is evident that individuals of mimicking 

 species must bear a very small proportion to the 

 mimicked (just as the latter to the whole insect 

 fauna), for if they became anything like equal to 

 them in numbers, the education of the enemies 

 would never be complete, and the whole mechanism 

 would break down. The theory of mimicry was first 

 brought forward by Bates in 1S62. The whole of 

 the conclusions above summarised are of the very 

 greatest interest ; the intimately related theories of 

 warning colours and protective mimicry, originally 

 due to Wallace'' and Bates respectively, and the later 

 developments of which we owe to Trimen, F. Midler, 

 Meldola and Poulton, furnish a complete and 

 beautiful explanation of the phenomena in question, 

 which must be admitted to form a compact mass of 

 the strongest possible evidence in favour of 

 Darwinism. 



A special kind of "Pseudaposematic colouration," 

 to which Mr. Poulton directs attention, is seen in the 

 case of various caterpillars possessing conspicuous 

 tufts of hairs, which tempt an enemy to bite at them, 

 only to get a mouthful of hairs for its pains, while the 

 caterpillar escapes ! Mr. Poulton kept a marmoset, a 

 chameleon and some lizards, which he seems to have 

 treated rather badly, inducing them to eat various 

 insects which he suspected of warning colouration, 

 etc.! "A caterpillar of the common, vapourer 

 moth {Orgyia antiqua), was introduced into a 

 lizard's cage, and when attacked, instantly assumed 

 the defensive attitude, with the head tucked in and 

 the ' tussocks ' separated and rendered as prominent 

 as possible. An unwary lizard seized the apparently 

 convenient projection; most of the 'tussock' came 

 out in its mouth, and the caterpillar was not troubled 



further. The lizard spent a long and evidently most 

 uncomfortable time in trying to get rid of its mouthful 

 of hairs " (pp. 198-99). On another occasion an 

 adult lizard refused to be taken in in this way ! 

 Similarly our author gave the chameleon a lesson 

 with a bee, which it did not forget. 



Various interesting examples of mimicry of other 

 kinds than that related to warning colouration, and 

 for both aggressive and protective purposes, are given 

 by Mr. Poulton, but we have no space to mention 

 any cases. 



In the chapter on " Colours produced by courtship,'' 

 Mr. Poulton argues strongly in favour of Darwin's 

 theory of sexual selection, and defends it from the 

 attacks of Wallace and others. He certainly appears 

 to have made out a very strong case, and his criticism 

 of Wallace's unsatisfactory and rather vague 

 alternative theory of the production of sexual 

 colour by "surplus of vital energy" etc., appears 

 most conclusive. One of his best points is that such 

 a theory does not in the least account for the 

 aesthetic value of such colours, which so distinctly 

 differentiates them from warning colours, for 

 instance, which are merely designed to be con- 

 spicuous. Nevertheless, as indeed the author admits, 

 there is no hard and fast line between the two 

 categories, one kind of colour being sometimes uti- 

 lised for the other purpose. And everyone is by no 

 means agreed as to the beauty or otherwise of some 

 warning colours. Thus considerable difference of 

 opinion prevails as to the beauty or crudeness of the 

 colouring of a tiger moth's wing, and many other 

 instances might be cited. And even if we grant the 

 existence of a widely -spread aesthetic sense among ani- 

 mals, we are confronted with the extremely difficult 

 question of its origin. Professor Ray Lankester thinks 

 this may be explained by supposing the power of dis- 

 tinguishing between light of different refrangibility 

 to be a primary function of the retinal cells, and 

 the stimulation of the brain caused by the incidence 

 of the different light rays to be a pleasant sensation, 

 normally accompanying the healthy activity of 

 nervous mechanism. But even if we admit this, we 

 are no nearer to an explanation of why what we 

 call harmonious grouping of colours should be 

 particularly pleasant to an insect. Mr. Poulton 

 argues that our own aesthetic taste has been largely 

 created for us by insects through the production of 

 the colours of flowers, and of their own sexual 

 colouration, by their selective action. He uses the 

 fact of the production of the former as evidence for 

 the production of the latter by the same means, but 

 the argument is hardly fair. It is, as Mr. Wallace 

 has shown, quite possible to explain the former on 

 the principle of recognition markings, without 

 supposing a special aesthetic sense at all ; and it 

 is obviously better to explain the one set of 

 phenomena by an intelligible principle, such as the 

 operation of natural selection, through the necessity 



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