722 THE MICROSCOPE. 



enamel, in the others they are of a horny nature. To the 

 Placoid order helong the Skates., Dog-fish, Ray, and Sharks ; 

 cartilaginous fishes, having skins covered with small prickly 

 or flattened spines. To the Ganoid helong the Sturgeon, 

 Lepidosteus, Hassar-fish, and Polypterus ; fishes of this 

 order are more generally found in a fossil state, and the 

 scales are of a bony character. To the Ctenoid belong the 

 Pike, Perch, Pope, Basse, Weaver-fish, &c. ; their scales 

 are notched like the teeth of a comb. To tbe Cycloid 

 belong the Salmon, Herring, Eel, Carp, Blenny, and the 

 majority of our edible fishes ; their scales are circular and 

 laminated. The scales of the Eel tribe are of an oval 

 figure, and are among the most remarkable that can be 

 selected for microscopic examination. To procure them, a 

 sharp knife must be passed beneath the epidermal layer, 

 and a portion of it raised, in a similar manner as directed 

 for tearing off the cuticle from plants : after a few trials 

 some will be detached. They are of an oval figure, rather 

 softer than the scales of other fishes, and in some parts of 

 the skin do not form a continuous layer. When the skin 

 has been stripped off, previous to the fish being cooked, 

 the scales can be obtained from the under surface, with a 

 knife or pair of forceps. The scales of the viviparous 

 Blenny are of a circular figure, situated under the epider- 

 mal layer ; they were described by Mr. Yarrell as mucous 

 glands, from their figure and small number. The surface 

 of the skin of this fish, when fresh, appears to be covered 

 with follicles ; if, however, a portion be scraped off, it will 

 be found to be a mass of delicate circular scales. A piece 

 of the skin, when dried, exhibits the scales to great 

 advantage, and, like those of the Eel, are beautiful objects 

 for polarised light. The prismatic colours exhibited by 

 fish are said to be due to the presence of fatty matter in 

 the skin ; but the beautiful metallic tints displayed by 

 so many of them are rather due to the numerous micro- 

 scopic plates, or scales, distributed over its surface. 



Having thus brought our brief examination of a few of 

 the more important structures of the animal economy to 

 a close, it only remains for us to express a hope that it 

 will be found to smooth the way, or in some degree assist 

 the investigations of the student to a better and more 



