FISH IN GENERAL. 81 



small thin scales, sunk in a thick epidermis, to the bony 

 shields which occur on the sturgeon, and the inflexible cuirass 

 of trunk-fish (ostracion), formed by their being soldered 

 together. The scales of fish consist of a corneous, and often 

 of a calcareous substance, chemically resembling the compo- 

 sition of bones and teeth. They are usually imbricated ; 

 that is, overlapping each other like tiles. Some are very 

 thick, entirely stony, very close, but scarcely overlaying, and 

 forming a real tigulated armour, as we find it in lepisosteus, 

 bichir, &c. In the species of eels, the scales are not con- 

 tiguous, but strewed very closely, and incrusted in the 

 epidermis. Turbots and cyclopteri, are provided w r ith some in 

 the form of cones or tubercles, adhering by their base with 

 naked spaces round them ; similarly formed scales, but re- 

 duced in size to small points, cover the body of most tetrodons. 

 In diodon these points become long spines, with an enlarged 

 basis to support them. The shai*p granulations on the skins 

 of dog-fish, and of most chondropterygians, are also a kind of 

 scales in the form of a rasp, which, when sufficiently close, 

 can be polished down, and become what is termed shagreen. 

 But the most complete scales, which show their affinity to 

 teeth, are the thorns on the back of rays ; their oval and 

 raised basis is hollow, and receives vessels to feed a pulpy 

 nucleus, greatly resembling that of a tooth. 



From the dermis is secreted beneath the scales, that bril- 

 liant silvery substance w r hich confers a metallic lustre upon 

 so many fish : it is composed of small laminae, resembling 

 burnished silver, capable of being removed by washing from 

 the skin or from the under surface of the scales, and with this 

 substance the well known false pearls are coated. In many 

 species of fishes it is likewise secreted in the thickness of the 

 peritoneum, and about the swim bladder. Scales extend 

 more or less upon the fins, and in the squamipinnae, the 

 dorsal and anal fins, are covered with them almost as com- 



vol. x. a 



