386 Fly-rods and Fly-tackle. 



outer side ; and by a contraction or expansion of its di- 

 ameter, thus changing its convexity and consequently its 

 refracting power, does it adapt itself when in health al- 

 ways to form its focus or, in other words, to produce a 

 distinct image at the same point, the retina. 



Does the eye of the trout possess this or any equiva- 

 lent property ? It does not. The lens is as spherical as 

 a buck-shot, and of a consistency so indurated as appar- 

 ently to preclude the possibility of any change of form. 

 Therefore, it seems to me trout must necessarily be quite 

 near-sighted, and consequently lack the power to distin- 

 guish details of form except within very narrow limits. 

 And it is believed that this defect in vision extends more 

 or less to all fishes ; for though I have myself dissected 

 the eye of the trout and one other variety of fish only, 

 still the treatises on comparative anatomy lead me to 

 believe that the eyes of all are constructed in substan- 

 tially the same manner. 



All this was believed to be quite true when written 

 some years ago. It is still believed to be quite true. 

 But the inferences which then might reasonably be 

 drawn from these facts, now require reconsideration 

 and limitation. We live and learn. The researches of 

 Beers have since shown that the eyes of fishes do pos- 

 sess an adaptability which gives distinct vision at all 

 distances. This is not accomplished by change in the 

 convexity of the image-forming lens, as in man and the 

 land vertebrates generally, since that lens in the fish is 

 so indurated as to preclude such change. It is another 

 illustration of the truth of the old proverb, "There is 

 more than one way to skin a cat," and is accomplished 

 by moving the lens itself bodily from or towards the 

 retina, as circumstances may require. Thus the fish's 



