INTRODUCTION. 



THE external characters of fishes in general are too well 

 known to require particular description. The form of the 

 body, however, is subject to great variety. In some, it is 

 short and rounded, almost spherical, as in the Globe Tetro- 

 don, vol. ii. p. 457 ; in others, elongated, as in the Eel ; 

 it is remarkably compressed in the Dory and Opah, and 

 depressed in the Flatfishes and Rays or Skate. The most 

 common form is that of a cylindrical body, more or less 

 pointed at each end, and slightly compressed at the sides : 

 the Mackerel, at page 137, as a familiar instance, may perhaps 

 be named as exhibiting the highest degree of elegance in 

 shape, and, when very recently taken from the water, is so 

 rich and so varied in its colour, as to be fairly entitled to be 

 considered one of the most beautiful among British Fishes. 



The surface of the body is in most instances covered by 

 numerous scales, which vary considerably in size and sub- 

 stance in different species. The great importance of these 

 productions of the skin, as the organs of protection and rela- 

 tion between the animal and the medium in which it resides, 

 has been more particularly enforced by M. Agassiz in his 

 most valuable researches on Fossil Fishes. The arrange- 

 ment of the scales exhibits considerable uniformity : the 

 almost vertical lines in which each series is placed, crossing 

 each other at an acute angle, resembles the letter X, the 

 scale on the lateral line forming the apex of both cones. 

 This arrangement may be observed in the species of Carp at 



