VISION IN FISHES. 37 



tion system of fly-fishing, thus found their theory : 

 " The form of the eye in fishes proves that they 

 are all very short-sighted ; so much so, that the 

 dense medium of water can have but small in- 

 fluence in extending their vision, which must be 

 further limited from the eye being covered by the 

 common skin of the head, in order to defend the 

 eye-ball, as there are no eyelids for this purpose 

 as in other animals. This indistinctness of vision 

 may be observed, by any one who will take the 

 trouble, in the gold and silver fish usually kept in 

 glasses. It is of considerable importance for the 

 angler to bear this indistinctness of vision in 

 fishes always in mind, as much of his success 

 must depend on being guided thereby. The 

 shadow, for example, which will be cast upon the 

 water by having the sun in his back, will have 

 the same effect in frightening the fish as if it 

 were, caused by a harmless sheep or a prowling 

 otter; and the poor fishes, being unable to dis- 

 criminate between friends and enemies, dart away 

 in terror at every shadow which crosses them. 

 The same indistinctness of vision will prove the 

 decided fallacy of the supposed art of the routine 

 angler, who fancies the fish are so well skilled in 

 the colours and forms of particular flies as to 

 refuse all other sorts on particular seasons and 



D 3 



