VARYING COLOURS IN FISHES. 81 



of terror, the dark olive, with golden sides, changed 

 to pale, for eighteen hours, when it suddenly re- 

 gained its former tints." (apud Yarrell, i. 103). The 

 slightest examination, however, of the observation 

 referred to by Mr. Couch, and which, taken from 

 Loudon's Magazine, will be presently adduced (see 

 p. 85), will, we think, show that it by no means 

 warrants the conclusion thus drawn from it. 



But whatever may be the cause of the pheno- 

 menon, its effects upon the safety and economy of 

 fish in the various coloured soils to which they are 

 exposed in rivers'-beds, ponds, &c, by affording 

 them additional protection from their foes, is very 

 apparent. Practical fishers have often remarked 

 this, and writers upon the finny race have made 

 the same observation. " Pike," says Mr. Jesse, in 

 his interesting Gleanings, " in muddy ponds have a 

 muddy colour, while those in a clear stream, with 

 a gravelly bottom, are beautifully speckled and 

 mottled." — (iii. 67-) Baron Dumeril, in his Lec- 

 tures on the Eel, states, " That the genus consists 

 of many species, whose colour varies according to 

 the colour of the bottom of the stream which they 

 frequent ; in dark mud being black, and in gravelly 

 bottoms greenish-white." — (apud Jess., i. 45.) And 

 more at length, Mr. Swainson — " The resemblance 

 between the colours of the flat fish, in general, to 

 those of the ground they repose upon is so admira- 

 bly ordered, as to claim both attention and admira- 

 tion. The upper surface, or that which is exposed 

 to view, and to the action of the light, is invariably 



F 



