THE COLORATION OF FISHES. 343 
ordinary Burn Trout (Salmo fario, Linn.) I believe to be com- 
paratively domestic. The Salmon at home is of a distinctly 
domestic tendency. But to the Salmon at sea, as to the other 
fishes congregating together in multitudes in the spawning season 
in the great deep, domesticity is a luxury that has been rendered 
impossible. These have either retrograded from, or have not 
advanced, and cannot afford to advance, to the civilisation of the 
shore fishes, when special sex coloration can be indulged in. 
All the causes indicated are therefore at work colouring the 
fishes of the seas and rivers; sunlight pre-eminent, surroundings 
and habitat in its train, protective colouring in many instances, 
and sexual desire for display and self-glorification to a greater 
extent perhaps than we know. There is here a wide field for 
interesting observation, and our shore fishes lend themselves 
readily to the investigation, 
