288 NATURAL HISTORY OF OUR SHORES 



This does not explain the case satisfactorily, for while 

 the little Elysia viridis, crawling upon and feeding upon the 

 spongy green weed, Codium tomentosum, is certainly of the 

 same colour, the Aplysia feeds on green Zoster a, and is 

 deep purple within and without, and plentifully furnished 

 with a purple dye ; Eolis feeds on red anemones chiefly, 

 and is usually white, sometimes grey. 



In the Cephalopods, however, we find an unmistakable 

 purpose, or rather service, in colour and coloration. 



Frequently I have watched an octopus crawling over 

 varied ground, and noticed that, as it passes over stones 

 and fucus. it puts on a corresponding colour an exact 

 imitation ; then as it traverses an intervening strip of white 

 sand or reddish gravel the colour changes instantly to the 

 required shade, the brown to be reverted to when the next 

 patch of rock or fucus is reached. 



Octopus has great control of colour. It has purple and 

 orange, but these are only put on when it is in safety ; 

 especially when, as it often does, it perches itself up on the 

 topmost bit of rock at hand. Especially after a good 

 meal does it put on this fancy dress, and glows with the 

 tints of satisfaction. 



Occasionally, for no apparent reason, it assumes 

 two colorations at once one side pale grey, the other 

 deep brown, the division central with mathematical 

 precision. 



The little Sepiola changes rapidly, just like the octopus. 

 Anyone watching it in a shallow pool must at once be 

 struck with this over sand white ; over gravel a little 

 corresponding speckling ; and then over rock or fucus all 

 the available pigment is forced to the surface, and it is as 

 brown as a ripe chestnut. 



Sepia and Loligo also change to suit surroundings, but 

 in a less marked way. Of course this is protective, for 

 they are eagerly sought for by large fishes, especially the 



