AND OF LIGHT. 257 



single plaice out of a large number upon a bright sandy 

 surface was dark-coloured, and Nicoll * noticed that in 

 addition to the light-coloured trout usually seen in a 

 chalk stream in Hampshire, very dark individuals occa- 

 sionally appeared. In both instances, however, it was 

 proved that the fish were blind, and therefore unable to 

 respond to the stimulus of reflected light. 



Besides the amphibia, fish, and reptile mentioned, 

 many other animals belonging to the same groups ex- 

 hibit a similar power of rapidly adapting their colour to 

 that of their surroundings. The power is also pos- 

 sessed by many invertebrate animals. It is probably 

 very common among Crustacea, and some cuttle fish 

 can modify their colours with extreme rapidity. In 

 Octopus vulgaris the protective resemblance is very 

 striking, and so completely is it under the control of the 

 nervous system that I have seen an individual change 

 its colour from a dirty white to a dark brown in less 

 than a second. It is amongst the Lepidoptera, how- 

 ever, that our knowledge has been furthest advanced. 

 The power of adaption has so far been proved to 

 exist in this group during the larval and pupal stages 

 only, though it is probable that a relatively small num- 

 ber of perfect insects also possess it.f Again, it is 

 present only in such pupse as are exposed, and has been 

 found wanting in those of moths which are as a rule 

 either buried in the earth or concealed in opaque 

 cocoons. Professor Poulton J has shown, however, 

 that the pupa of the Swallow-tailed moth forms an ex- 



* " Colours of Animals," p. 86. 

 t " Colours of Animals," p. 110. 

 $ Ibid., p. 111. 



