XVI 



LIFE on the solid earth is a grim struggle for most 

 Nature's animals the stronger ever preying on the 

 camouflage wea fc er> Yet for mammals, at least, the 

 odds are perhaps in favour of each individual surviv- 

 ing to a respectable age (except where man interferes 

 to upset the balance), for the majority of terrestrial 

 mammals subsist on herbs or fruit. But it is otherwise 

 in the world of waters. Life on the ocean wave is a 

 fine affair, but beneath the waves it is one unending 

 scene of rapine and violent death. Very few fishes are 

 vegetarian feeders ; all but an infinitesimal number are 

 incessantly pursuing or flying for their lives. In order, 

 therefore, that no species should be exterminated (a 

 disaster against which Nature makes constant provision, 

 however indifferent she may show herself to the fate of 

 individuals), it might be expected that the food fishes 

 which are most liable to attack from powerful enemies 

 should have had protective colouring bestowed on them. 

 And such we find in many species, the flounder, the 

 sole, and flat fishes in general, not only have their upper 

 surfaces painted in exact resemblance to the sand, ooze, 

 or gravel whereon they may make their lair, but they 

 are actually endowed with the property of automatically 



