84 Animal Life and Intelligence. 



or figured isolated from their surroundings. The zehra is 

 a sufficiently conspicuous animal in a menagerie or a 

 museum ; and yet Mr. Galton assures us that, in the bright 

 starlight of an African night, you may hear one breathing 

 close by you, and be positively unable to see the animal. 

 A black animal would be visible ; a white animal would be 

 visible ; but the zebra's black and white so blend in the 

 dusk as to render him inconspicuous. 



To cite but one more example, this time from the 

 invertebrates. Professor Herdman found in a rock-pool 

 on the west coast of Scotland " a peculiarly coloured speci- 

 men of the common sea-slug (Doris tuberculata) . It was 

 lying on a mass of volcanic rock of a dull-green colour, 

 partially covered with rounded spreading patches of a 

 purplish pink nullipore, and having numerous whitish 

 yellow Spirorbis shells scattered over it the general effect 

 being a mottled surface of dull green and pink peppered 

 over with little cream-coloured spots. The upper surface 

 of the Doris was of precisely the same colours arranged in 

 the same way. . . . We picked up the Doris, and remarked 

 the brightness and the unusual character of its markings, 

 and then replaced it upon the rock, when it once more 

 became inconspicuous." * 



Then, too, there are some animals with variable pro- 

 tective resemblance the resemblance changing with a 

 changing environment. This is especially seen in some 

 Northern forms, like the Arctic hare and fox, which change 

 their colour according to the season of the year, being 

 brown in summer, white and snowy in winter. The chamse- 

 leon varies in colour according to the hue of its surround- 

 ings through the expansion and contraction of certain 

 pigment-cells ; while frogs and cuttle-fish have similar but 

 less striking powers. Mr. E. B. Poulton'sf striking and 

 beautiful experiments show that the colours of caterpillars 



* Proceedings Liverpool Biological Society, 1889. 



t Since this chapter was written, Mr. Poulton has published his interesting 

 and valuable work on "The Colours of Animals," from which I have con- 

 trived to insert one or two additional examples. 



