February 13, 1896J 



NATURE 



353 



the time has arrived when this may — nay, must be allowed, if 

 our science, with its immense wealth of raw material, is to take 

 that rank to which it is entitled among the departments of 

 modern biology. If, as is undoubtedly the case, the speculative 

 method has been found fruitful in other fields of natural history, 

 it behoves us as co-workers in the great battle for truth to re- 

 examine our weapons — to ask ourselves seriously whether the 

 time and energy of our most active workers is being utilised in 

 the best way for the advancement of knowledge. 



To many it may appear that the use of hypothesis as a guide 

 to investigation is so obvious, that no special advocacy is re- 

 quired. All I have to say, in this case, is to express the earnest 

 wish that the Fellows of this Society who hold such a view may 

 be numerous — the more numerous the better. I will venture to 

 remind you, however, that my predecessor in this chair has 

 stated, with respect to this method of handling entomological 

 problems : 



" I feel, however, for myself, and I think that others must 

 also feel, that however great and important is the knowledge 

 which we may ultimately attain, by endeavouring to discover 

 the laws which govern the development, variation, and distri- 

 bution of insects, the knowledge we have of the actual facts is 

 in many cases quite insufficient to bring such speculations to a 

 definite end. 1 also feel that the number of persons whose 

 talents are sufficiently great to enable them to steer a straight 

 course through the numerous difficulties, contradictions, and 

 doubts which constantly surround such inquiries is very limited " 

 {Proc. Ent. Soc. 1893, p. xlvi.). 



I am sure Mr. Elwes will not ascribe any personal motive to 

 me in making use of this passage, as representing the views of 

 what may be called the conservative school of entomologists. I 

 feel only too acutely the truth of his remark that many agree 

 with him in this opinion ; at the same time I am sanguine 

 enough to believe that there are many who do not, and on behalf 

 of this constituency I have felt it a duty to urge a claim for the 

 speculative method, not as displacing the older method of col- 

 lecting and recording facts altogether, but as a stimulus to more 

 systematic investigation, rendered imperative by the general 

 advance of Inological science. For my own part, I believe that 

 the time has gone by when every attempt at discovering natural 

 law in the organic world by the aid of entomological observations, 

 is to be met by this prevalent cry of non possunitis. 



If we turn to results as a measure of the value of methods, 

 it will, I imagine, be conceded that we can show good cause 

 in favour of theorising. I may be permitted to draw some 

 illustrations from the Lepidoptera, the only order to which I 

 can lay claim to some slight special knowlege, and in which our 

 former President is a recognised authority. In the following 

 remarks I desire most emphatically to dissociate myself from 

 controversial matters, because my sole aim in this address is 

 to clear the atmosphere for the more healthy use of the specu- 

 lative faculty by our younger and rising workers. I wish it to 

 be understood that in speaking of any particular hypothesis, I 

 am not now raising the question of its soundness or unsound- 

 ness — that is, logically, a distinct issue — but I am simply 

 adducing the hypothesis in order to illustrate the results of its 

 introduction into modern scientific thought. I begin with the 

 phenomena of mimicry and protective resemblance among 

 butterflies and moths as first explained by our late distinguished 

 Fellow and past President, Henry Waller Bates, in his memor- 

 able pa]>er of 1861, which was followed by the well-known 

 memoirs of Wallace and Trimen on the same subject. It will 

 be remembered by all who are familiar with the history of the 

 subject, that this was the first application of the theory of 

 natural selection of Darwin and Wallace to explain a new set 

 of phenomena. It was a speculation evolved by Bates, not 

 when collecting in the Amazon Valley, as is generally supposed, 

 but while looking over his specimens when he had reached 

 London, and was pondering, at his f)wn fireside, over the mean- 

 ing of the remarkable superficial resemblances among the 

 butterflies of different groups which he had brought home. ' 



The Batesian theory was fruitful ; it carried with it the 

 explanation of the resemblance between insects of distinct 

 orders and of the assimilation of insects and other animals 

 in colour and form to the objects among which they lived ; it 

 prompted further observation and experiment because more evi- 

 dence was required as to the protected character of the insects 

 which were copied ; it raised the whole question of the exist- 

 ence of such protected species in nature, and the question has been 



' I owe this statement to Mr. Bates himself, who has often made it to me. 



an.swered so far in the affirmative, although there is still a large 

 field for further experimental observation waiting to be explored. 

 The facts have increased enormously since 1861, the search for 

 new instances having lieen stimulated by the explanation sug- 

 gested by Bates, and the syslematist is now no longer in danger 

 of being deceived by superficial resemblances. 



The theory of Bates left unexplained the resemblance between 

 species belonging to protected groups to which he had himself 

 called attention in his original paper ; an extension was required 

 and was made by our Hon. Fellow, Fritz Miiller in 1879, and 

 as a result, whether this extension be considered valid or not — 

 a point which I am not now raising — the systematist is now more 

 fully alive to the superposition of external similarity upon struc- 

 tural resemblance due to true blood-relationship, as can be seen 

 from the writings of Moore on the genus Eiiphea, and of Wood- 

 Mason and others on certain Papilionidiie. As another result of 

 Fritz Midler's hypothesis, the question of inherited knowledge 

 of edible and inedible species on the part of insect-eating 

 creatures has likewise been raised, and has already led in the 

 hands of Prof. Lloyd Morgan to some interesting experimental 

 conclusions. 



As the product of a theory we thus have a large body of real 

 and tangible knowledge gleaned from nature ! Mere casual 

 observation would never have revealed the widespread existence 

 of the phenomenon if the stimulus to look out for it had not 

 come from the theoretical side. 



It is not the bare record of the comparatively few cases of 



mimicry that constitutes the highest value of these classical 



memoirs— it is the speculation, the hypothesis, the suggested 



I cause of the phenomenon that has given vitality to what 



would otherwise have been a disconnected and meaningless 



set of facts. But the consequences of the introduction of the 



theory of natural selection into the subject of insect colouration 



have not yet l^en exhausted. From the observation that the 



species which are mimicked are generally gaudily coloured and 



take no special means to hide themselves, it is but a step to the 



well-known theory of warning colours propounded by Wallace in 



1867. That theory, in itself the outcome of a question raised by 



Darwin in connection with his theory of sexual selection, 



stimulated the experiments of the late Jenner Weir and of A. G. 



Butler, the striking observations of Thomas Belt in Nicaragua, 



\ the detailed researches of Weismann into the origin and meaning 



j of the colours of caterpillars, and the later systematic series ot 



I experiments conducted by Poulton. Vet another example I will 



permit myself to make use of because it is one in which I have 



i some personal interest. In considering the subject of adaptive 



I colouration as explained by Bates and Wallace, a difficulty 



occurred in the case of species which are of variable colouring : 



I ventured to suggest, as far back as 1873, that this kind ot 



; colouring would be explicable by natural selection, if we supposed 



I that this agency could confer a power of adaptability on the 



I individual. At that time no mechanism could be conceived of 



': by which such individual adaptability could be acquired, excepting 



! the direct assimilation of the colouring- matter of food-plants in 



; the case of caterpillars or other vegetable feeders. This, of 



I course, carried with it the implication that natural selection could 



j work on physiological processes if they were of use, just as well 



I as upon any external morphological character. Stimulated by 



I this hypothesis, other cases of variable colouring were sought for 



and found. The subject was later taken up by Prof. Poulton, 



who, for many years, conducted experiments and obtained 



results which are now familiar to all naturalists. The original 



speculation, that variable colouring was the result of an individual 



adaptability due to natural selection, implies that this faculty is 



of bionomic value. I am not now concerned with the validity or 



otherwise of this assumption ; that is an issue on which opinion 



appears to be divided ; although, I have no doubt in my own 



mind on the point, it is not necessary to state the case with any 



bias on the present occasion. Now the experiments of Poulton 



have shown that this colour variability is of very much more 



frequent occurrence than was ever dreamt of in 1873, and his 



facts have, in the main, been substantiated by the independent 



observations of many other experimenters. And it turns out also 



that the mechanism of the process is not even the simple 



a.ssimilation of colouring-matter from the food-plant, excepting 



in the case of green caterpillars, in which it has been shown that 



chlorophyll in a modified form passes into the blood. The 



colour variability of caterpillars and pupte in response to the 



external stimulus exerted by coloured surfaces, as established by 



these experiments, has brought us face to face with a fundamental 



NO. 1372, VOL. 53] 



