60 INTRODUCTION. 



and placed above each other in successive layers, 

 each of which can be separated by maceration in 

 water. When the enamel is present, it generally 



forms a thick layer above these. They are often 

 transparent, and transmit the bright colours and 

 metallic tints which are secreted beneath them, 

 while the different manner in which the layers 

 are deposited, give rise to many of the figures we 

 see, as it were imprinted, on their surface. A few 

 species have the skin nearly smooth, and appa- 

 rently defenceless, and without scales or plates. 



The scales are held in position by a fold of the 

 epidermis, often so delicate as scarcely to be 

 visible, but which covers almost the whole part of 

 the fish exposed to our view. They fold over 

 each other in different modes of imbrication, 

 sometimes regularly like the tiling of a house, 

 sometimes in a lateral form, or with the lower 

 longitudinal edge folding over the upper edge of 

 the scale below ; sometimes alternately, so that 

 the joining of the preceding scale is opposite the 

 centre of that which follows, while in others 



