VIII ORIGIN AXD USES OF COLOUR IX ANIMALS 209 



Professor E. S. Morse of Salem, Mass., found that most 

 of the Xew England marine mollusca were protectively 

 coloured ; instancing among others a little red chiton on rocks 

 clothed with red calcareous algas, and Crepidula plana, liv- 

 ing within the apertiu'es of the shells of larger species of 

 Gasteroi)ods and of a pure white colour corresponding to its 

 habitat, while allied species living on seaweed or on the 

 outside of dark shells were dark brown. ^ A still more 

 interesting case has been recorded by Mr. George Brady. He 

 says: "Amongst the Xullipore Avhich matted together the 

 laminaria roots in the Firth of Clyde were living numerous 

 small starfishes (Ophiocoma bellis) which, except when their 

 writhing movements betrayed them, were quite undistinguish- 

 able from the calcareous branches of the alga ; their rigid 

 angularly twisted rays had all the appearance of the coralline, 

 and exactly assimilated to its dark purple colour, so that 

 though I held in my hand a root in which were half a dozen 

 of the starfishes, I was really unable to detect them until 

 revealed by their movements."^ 



These few examples are sufficient to show that the principle 

 of protective coloration extends to the ocean as well as over 

 the earth ; and if we consider how completely ignorant we 

 are of the habits and surroundings of most marine animals, it 

 may well happen that many of the colours of tropical fishes, 

 which seem to us so strange and so conspicuous, are really 

 protective, owing to the number of equally strange and 

 brilliant forms of corals, sea-anemones, sponges, and sea- 

 weeds among which they live. 



Protedmi hy Terrifying Enemies. 



A considerable number of quite defenceless insects obtain 

 protection from some of their enemies by having acquired a 

 resemblance to dangerous animals, or by some threatening or 

 unusual appearance. This is obtained either by a modifica- 

 tion of shape, of habits, of colour, or of all combined. The 

 simplest form of this protection is the aggressive attitude of 

 the caterpillars of the Sphingidae, the forepart of the body 



^ Proceedings of the Boston Sac. of Nat. Hist., vol. xiv, 1871. 



- Nature, 1870, p. 376. 



P 



