ADDITIONAL NOTES. 291 



most of all, I believe its outer lamina; for if the scales be 

 triturated so as to rub off this portion, their lustre is diminished ; 

 and if incinerated some that have been triturated before 

 exposure to fire, others that have not been so treated a dif- 

 ference will be perceived in them on microscopical examination ; 

 those not triturated seem to be composed of a milky white part 

 attached to another of a light brownish hue, whilst those that 

 have been triturated consist, with few exceptions, of the latter. 

 The brownish hue seems, from the trials I have made on it, to 

 be owing to the presence of a minute portion of iron. The 

 scales, it must be kept in mind, are more or less transparent, 

 allowing the colouring matter, on which the hues and spottings 

 of the fish depend, to be seen through them. Accordingly, as 

 this subjacent colouring matter varies in its hues, so will the 

 general colour of the fish vary. In well-fed fish, the abdomen 

 of which is so silvery, there is both on the outer and inner 

 surface of the cutis a layer of white matter reflecting a pearly 

 lustre ; and the cutis itself being transparent, it is to this matter 

 as much as to the scales, or perhaps even more, that the silvery 

 hue of the part- is owing. It is instructive to examine the skin 

 in part deprived of its scales, and in part with them remaining 

 on, especially if dried on glass. So prepared, it is manifest how 

 little the scales have to do with its colouring, and the degree in 

 which they are concerned with its lustre. These remarks are 

 derived from the examination of the scales of the smolt and of 

 the young trout, and are applicable I believe to those of the full- 

 grown fish of each kind. In the instance of the full-grown 

 salmon, that portion of the fish which is most silvery, owes its 

 lustre in great measure to the abundance of scales and the 

 manner in which they overlap ; where thickest, two or three, 

 one over the other, may be detached from the same spot. When 

 their animal matter is consumed by fire, and they are viewed 

 under the microscope, their upper surface is seen to be more 

 brilliant than their under, and to exhibit a linear or ridgy 

 structure which is hardly, if at all, to be seen in the under. 

 When the phosphate of lime is removed by an acid, the appear- 

 ance under the microscope is such as to give the idea in accord- 

 ance with the preceding, that there is forming on the upper 

 surface a furrowed layer or lamina which the under is destitute 

 oij and less lustrous and pearly in consequence. J. D. 



