COLORATION 



217 



about among pieces of driftwood, and so close was the resem- 

 blance that it was almost impossible to pick out the living 

 fishes from the fragments of wood. Young Half-beaks [Hemi- 

 rhamphus) appear very like pieces of seaweed when observed at 

 the surface of the water, and it is said that when a net is passed 

 over the water in their vicinity, or when they are otherwise 

 alarmed, they at once become quite rigid, floating about in 

 any position and apparently in a helpless, inanimate condition. 

 Similar cases of mimicry might be multiplied indefinitely, but 

 one more must suffice. Dr. Beebe has described some Slender 

 File-fishes {Monacanthus) feeding among clumps of eel-grass. 



Fig. 87. 

 Alonocirrhus poly acanthus, X i . 



and notes that when poised head downwards with the fins 

 gently waving in the water, the general tapering form of the 

 body, together with the undulating fins and mottled green 

 colour, gives them a remarkable resemblance to a frond of 

 seaweed or blade of the grass (Fig. 88) . 



The variation in colour found among individuals of the same 

 species has already been mentioned, and in such a form as 

 the common Brown Trout {Salmo trutta) of our own rivers and 

 streams, the connection between a particular type of coloration 

 and the nature of the surroundings is often striking. Dr. Giinther 

 has observed that "Trout with intense ocellated spots are 

 generally found in clear rapid rivers and in small open Alpine 



