1873.] COLOURING IN INSECTS. 161 



or for other purposes, would be certainly benefited by being able to 

 assume the colour of any locality in which it might find itself. 

 Here natural selection works, as before, in producing and maintain- 

 ing a power to change colour, it being quite immaterial to this 

 agency at what period of the insect's life the change of colour is 

 induced, whether it only occurs in individuals born in the district, 

 or in individuals that have roamed into the district in the perfect 

 state and undergone subsequent change. So also is natural selec- 

 tion regardless, in these cases, whether the disguising colour is con- 

 genital or consequent on the emergence from the pupae, whether it 

 is a colour exposed by ecdysis or one due to actual change of tint in 

 the tissues — regardless also whether the change is voluntary or in- 

 voluntary on the part of the insect. 



The examples adduced from classes of animals other than insects 

 are capable of being reasoned upon in a precisely similar manner ; 

 but it is needless here to extend the argument. 



The results of this inquiry have thus led me to conclude that the 

 cases which I have grouped under Class V. are cases which differ 

 from ordinary protective resemblance, inasmuch as the primary vari- 

 ations are indubitably produced by direct action, but controlled and 

 accelerated by natural selection. As the particular manner in which 

 these original variations are produced is, in nearly all these instances, 

 quite unknown, the observation made at the outset, that the study 

 of these cases "offers a wide and interesting field for observation," 

 is, I think, fully justified. The part played by natural selection in 

 the production of the class of cases I have here discussed is thus in 

 some degree analogous to the function ascribed to this agency by 

 Mr. Herbert Spencer in the formation of the woody vessels iu trees* 

 — that, viz., of an accelerator and controller of results primarily due 

 to what this philosopher has, in mechanical terms, called " direct 

 equilibration " f. 



In conclusion I beg leave to present in a tabular form the results of 

 the classification above set forth, so as to include Class V., and thus 

 embody all the known cases of protective resemblance. The classi- 

 fication refers, as before, to the object imitated ; but it is to be 

 understood that the " object imitated " and the " disguising cha- 

 racters " of the species are convertible terms. A change in character 

 witnessed in the object simulated in passing from one district to 

 another, or in the same district, is termed for brevity a variation 

 "in space," while a change occurring in the course of time is termed 



* " On Circulation and Formation of Wood," Trans. Linn. Soc. vol. xxv. 



t The inquiry has suggested itself whether there might not occur conditions 

 under which a case of ordinary protective resemblance might be mistaken for a 

 case of Class V. It seems probable at first sight that natural selection would 

 be able to produce local modifications in the disguising characters of protected 

 species corresponding to local changes in the characters of the imitated object. 

 Such local modifications might occur in districts so situated as to prevent inter- 

 change of species ; but in contiguous districts presenting facilities fur intercom- 

 munication it seems to me that crossing would entirely prevent the formation 

 of local varieties by natural selection, unless this agency were aided by "direct 

 action," under which circumstances we should have an example of Class V. 



Proc. Zool. Soc— 1873, No. XI. 11 



