290 



NATURE 



[July 24, 1890 



even the colour of the blood is entirely changed in the 

 passage from a green to a dark variety, or vice versa. 

 Hence it is to be expected that the changes occurring in 

 an insect will occupy a considerable time as compared 

 with those which take place in a frog. Another differ- 

 ence between the two processes is that the stimulus from 

 the environment falls upon the eye in the one case, and 

 probably upon the surface of the skin in the other." 



Mr. Poulton's work is of special importance for the 

 numerous experimental proofs he gives of the protective 

 value of many of the peculiarities in the colour markings 

 or attitudes of insects. Thus the green lizard {Lacerta 

 viridis) generally failed to detect a " stick caterpillar " 

 in its position of rest, although the insect is seized and 

 greedily devoured directly it moves. The value of the 

 tufts of hair, called "tussocks," on many caterpillars 

 was also proved experimentally. 



" A caterpillar of the common vapourer moth {Orgyia 

 antiqud) was introduced into a lizards' 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." 



There is a most excellent account of the larva of the 

 lobster moth {Siatiropiis fagi) which is protected by its 

 marvellous resemblance to a withered beech-leaf and its 

 stipules, and is also able to assume a terrifying attitude, 

 when it resembles some large and strangely formed 

 spider. When one of these larvae had assumed the terri- 

 fying attitude, a marmoset monkey was much impressed 

 by the alarming sight, and only ventured to attack after 

 the most careful examination, and even then in the most 

 cautious manner. A lizard exhibited the same caution 

 before the larva was attacked. The same insect is also 

 to some extent protected from ichneumons by two black 

 marks, exhibited only when attacked, which resemble 

 those produced by the stings of ichneumons, and thus 

 prevent an attack, since these parasites always avoid 

 larvae which are already occupied. 



Two chapters are devoted to an excellent account of 

 the various forms of mimicry, a subject which, however 

 interesting, has been so often treated that there is com- 

 paratively little new to be said upon it ; and then we 

 have two chapters on sexual colours, which will offer 

 material for a few remarks, as the whole subject is full of 

 difficulties, and requires much more observation and ex- 

 periment before the problems it presents can be satis- 

 factorily settled. 



Mr. Poulton fully accepts Darwin's theory of female 

 choice as the source of the greater part of the brilliant 

 colour, delicate patterns, and ornamental appendages 

 that exist among animals, and especially among birds 

 and insects. Much stress is laid on the observations of 

 two American writers on the courtship of spiders. These 

 show that spiders resemble birds in the strange postures 

 and long-continued antics of the male during courtship, 

 and that he always exhibits whatever portion of his body 

 is most conspicuously coloured. 



" The female always watches the antics of the male 

 intently, but often refuses him in the end, ' even after 



NO. 1082, VOL. 42] 



dancing before her for a long time.' Such observations 

 strongly point towards the existence of female preference 

 based on aesthetic considerations." 



To the last four words we demur, as being altogether 

 unproved. Why (esthetic considerations? Why not a 

 deficiency in activity, or in size, or in some exciting 

 odour, or in the excitability of the female at the moment? 

 Any of these causes, or others unknown to us, may de- 

 termine the acceptance or rejection of a male spider ; 

 and it is to be noted that the long-continued and careful 

 observations of these American authors have not enabled 

 them to adduce a single case in which any deficiency of 

 colour was observed in a rejected male. There is, indeed, 

 one case in which two well-marked male varieties of a 

 species exist — one red, the other black ; and these assume 

 different attitudes in courtship. Messrs. Peckham say : 

 " the niger form, evidently a later development, is much 

 the more lively of the two, and whenever the two varieties 

 were seen to compete for a female, the black one was 

 successful." On this Mr. Poulton remarks : " It must be 

 admitted that these facts afford the strongest support to 

 the theory of sexual selection " ; but there is not a particle 

 of proof that the black colour was the cause of the selec- 

 tion rather than the "superior liveliness" which all 

 breeders of animals believe to be the most attractive 

 characteristic a male can possess. 



Mr. Poulton speaks continually of the possession of an 

 "aesthetic sense by those creatures in which sexual 

 ornament occurs, but no proof whatever of this is given, 

 other than the fact that insects do recognize diversities of 

 colour, and that a few birds collect bright objects, as in 

 the case of the bower-birds. This habit, existing in a 

 few species only of one of the highest groups of birds, 

 can hardly be held to be a proof that in all birds, even 

 in such comparatively low types as ducks and Gallinacese, 

 slight variations of colour in the male determine the 

 choice of the female. 



This aesthetic sense is supposed to exist even in 

 insects, and some very doubtful facts are alleged in sup- 

 port of this view. It is stated that if all the brightly- 

 coloured butterflies and moths in England were arranged 

 in two divisions, the one containing all the beautiful pat- 

 terns and combinations of colours, the other including 

 the staring, strongly-contrasted colours and crude pat- 

 terns, we should find that the latter would contain, with 

 hardly an exception, the species in which independent 

 evidence has shown, or is likely to show, the existence of 

 some unpleasant quality. The former division would 

 contain the colours displayed in courtship and when the 

 insect is on the alert. And it is added that there is an 

 immense difference between the two divisions — the one 

 most pleasing, the other highly repugnant, to our eesthetic 

 sensibilities, because the pleasing colours have been de- 

 termined by the insect's sense of what is beautiful., the 

 displeasing colours by the need for what is conspicuous to 

 a vertebrate enemy. If there is, indeed, any such great 

 and constant difference due to these causes, it must exist 

 in all countries, and in all groups where these causes 

 have come into play ; but it is very doubtful whether any 

 such difference does exist. In looking over a genera^ 

 collection of butterflies few would decide that the 

 Danaidae, Acrasidae, and HeUconidae showed any deficiency 

 in beauty and harmony of colour ; yet they are pre- 



