306 PHILOSOPHY OF ZOOLOGT. 



The SKIN of fishes consists, as in the other vertebral ani- 

 mals, of a true skin, a rete mueosum, and a cuticle. The 

 cerium is remarkably thick in those species which have 

 small scales ; while in those which have large scales, it fre- 

 quently assumes the appearance of a thin membrane. It is 

 much more closely attached to the muscles in this tribe 

 than in any of the other vertebral animals. This organ, in 

 the cod, for example, consists almost entirely of gelatine, 

 and is much esteemed as an article of food, and is used also 

 in fining, as a substitute for isinglass. Eel-skins are like- 

 wise used in the manufacture of size, in consequence of 

 the gelatine which they contain. There is no appearance 

 of the corpus papiUare or villous surface. The mucous 

 web is remarkable for the brilliant tints which it exhibits 

 in many species, communicating to the incumbent scales 

 their peculiar lustre. 



The cuticle appears in fishes in a soft state, and, in many 

 instances, i& a simple mucous substance enveloping the 

 body. It is detached at certain seasons of the year in large 

 pieces. The scales are implanted in this layer, and, in their 

 position, the facility with which they are reproduced, and the 

 purposes which they serve, resemble the hairs on the skins of 

 quadrupeds. They cover the body of fishes like tiles on the 

 roof of a house, pointing backwards. The posterior edge, 

 which in general is free, is usually crescent-shaped, fringed 

 in some species, and smooth in others. By means of a lens, 

 longitudinal ribs may be perceived finely decussated by trans- 

 verse striae. These ribs sometimes radiate from the centre, 

 and the crossing striae are concentric. When macerated in 

 weak acids, they are found to consist of alternate layers of 

 membrane and phosphate of lime, and hence are supposed 

 to increase in every direction by the addition of new 

 layers. 



