290 ADDITIONAL NOTES. 



they are not familiar with, or know only as enemies. By means of 

 three powerful muscles, their movable eyes can be either with- 

 drawn into their deep sockets or made more prominent, and can 

 be turned in any direction ; and the lens, from its yielding 

 nature, may have its form that of a perfect sphere more or 

 less changed, more or less compressed and flattened ; and, in 

 addition to a fine mechanism of the ball in its several parts, the 

 eye has a very large optic nerve of a magnitude, indeed, extra- 

 ordinary compared with the small mass of brain. 



For success in angling, too much attention cannot be paid to 

 the power of sight of the fishes of this family. As a general rule, 

 it may be laid down, that he who fishes with the longest line 

 who can keep most out of sight, will take the largest number, 

 and fish of the largest size. Even when the light is obscure, as 

 at the time of advanced summer twilight, the visual faculty of 

 the trout seems to be little less powerful than in broad daylight, 

 as if it had the power which it probably possesses of adapt- 

 ing its eye to the degree of light ; a power, it may be remarked, 

 very suitable to its habits of feeding at night as well as by 

 day. J. D. 



( On the Colouring of the Salmonidce, j 



It has been observed that the colouring of the trout as 

 well as its form depends a good deal on its condition; that 

 when well fed, it has a smaller head and more rounded body, 

 and a more silver} 1 - lustre. The smaller head and more rounded 

 and larger body considered merely proportional, [the latter 

 liable to augmentation from deposition of fat, from which the 

 other is exempt,] requires no comment. The more silvery hue 

 of the well-fed fish seems to depend on many circumstances 

 connected with its organisation, especially its scales and other 

 integumentary parts, and the adipose matter beneath them. The 

 scales have some resemblance to pearls in their composition, 

 consisting of membrane not soluble in muriatic acid, and 

 destructible by fire, and of phosphate of lime, soluble in the acid 

 and resisting the fire. After the separation of the phosphate of 

 lime by an acid, or of the animal matter by fire, the form of the 

 scale remains with its peculiar linear markings, denoting a con- 

 centric growth, but the pearly lustre in each instance is lost. 

 The scale, undoubtedly, is one cause of the silvery hue, and, 



