THE TROUT JUMP. 31 



most beautifully coloured fish are coral-feeders, dwelling 

 among the reefs and feeding off the bright polypes and 

 other beautiful creatures which abound in tropical seas. 

 This case is again quite paralleled by that of birds 

 and insects ; for the most gaily coloured species, like the 

 butterflies, rose-beetles, humming-birds, parrots, loris, 

 and toucans, are flower-feeders or fruit-eaters ; and we 

 may well suppose that in every case a taste for colour 

 has been aroused in the creatures themselves during 

 their constant intercourse with brilliant surroundings and 

 their continual quest for brilliant kinds of food. There 

 seems to be, in fact, a regular gradation of colour-sense 

 and colour-beauty in fishes, the most highly perceptive 

 being themselves apparently the most ornamented. 

 There is also a similar gradation of general sight- 

 faculties : from the case of a tropical shore-fish which 

 can thrust its moveable eyes out of their sockets, and 

 which hunts crustaceans out of water on mud-flats at 

 ebb tide, or of an open-sea fish which swims half above 

 the surface, and has its eyes divided horizontally into 

 two portions, one adapted for vision in air and the other 

 in water to the blind fishes of the Mammoth Cave and 

 of the marine abysses revealed to us by the explorers in 

 the Challenger. From all these converging indications 

 it is perhaps possible to make a nearer guess at the 

 visual faculties of fishes than most people would be at 

 first sight inclined to suspect. 



