66 



and salmonoids, and in the herring tribe : in the menhaden 

 this layer is thick, hard and blubber-Hke. 



The scales are modifications of the dermis, and are, ordi- 

 narily, thin, transparent, horny plates, with rounded quad- 

 rangular outlines, which are partially imbedded in folds or 

 pockets in the dermis, and covered by the epidermis, through 

 which, however, their tips protrude. The scales are usually 



10 



Section of the Skin or a Fish. 



a. Epidermis, b. Scales, c. Dermis 



imbricated, overlapping each other like the shingles on a roof, 

 but are sometimes separate and imbedded and partly hidden 

 in the skin, as in the eel. 



In fishes which live near the bottom and among the rocks, 

 such as the sea bass, red snapper, sheephead and perch, 

 the scales are usually thick, hard, closely imbricated and 

 deeply set in their sheaths, forming a strong coat of mail. 



In fishes which live in the mud, such as the tautog, the 

 burbot and the carp, the scales are usually covered by thick 

 layers of epidermis and mucus. 



In fishes which swim free and far from shore, such as the 

 herrings and the lake white-fishes, the scales are attached 

 merely by a small area of their rims, and being but slightly 

 covered by the epidermis, are easily rubbed off. Scales thus 

 removed are in many fishes easily renewed. 



The smooth polished surface of the closely set scales offers 

 little resistance to the motion of the fish as it glides smoothly 

 through the water. 



The exposed surface of the ordinary fish scale is usually 

 covered with a thin silvery coating, which derives its brilliant 



