THE SENSE OF NUMBER 23 



in the fly he does not, as so many artists depict him as 

 doing, snap it. He expands his gills so as to induce an 

 entering current through his open mouth, which carries 

 fly or nymph in with it. Therefore he has no need to see 

 the detail of his food very clearly in order to take it in. 

 May it not be that this defective near vision when con- 

 centrating on the fly is the correlative of the distortion of 

 the eye from its more general business of keeping a watch 

 for possible enemies ? 



Whether it is so or not I am not prepared to say. I am 

 no optician; but if some angler who is an optician would 

 make a study of this subject, and could deduce from his 

 anatomy of the eye of the trout the truth of this matter, 

 he might be conferring upon anglers some knowledge worth 

 having. 



VI 



THE SENSE OF NUMBER 



If the conclusion from my argument be accepted that 

 trout have a defective sense of form, and will often take 

 for a fly something that is either so tumbled or so differently 

 arranged from the natural insect it is supposed to represent 

 as to be very unlike it to the eye of man, the reader will 

 have no difficulty in accepting the corollary conclusion 

 that with the sense of form (and probably from the same 

 cause) the sense of number is also at fault. Countless 

 writers have poured scorn on the imitation theory, because 

 the hackle of a winged fly suggests many more legs than 

 the natural insect possesses. I suggest that the fish gets 

 only a general effect, and that, provided the excess of hackle 

 be not so pronounced as to spoil the general effect by 

 producing an appearance of clotting, it will not be fatal to 

 the fish taking the artificial fly for a natural fly. 



