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. 347 ; in others, elongated, as in the Eel ; it 

 is remarkably compressed in the Dory and Opah, and de- 

 pressed in the Flatfishes and Skate. The most common 

 form is that of a cylinder, more or less pointed at each end, 

 and slightly compressed at the sides : the Mackerel, at page 

 121, as a familiar instance, may perhaps be named as exhi- 

 biting 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 



