Recherches sur les Poissons Fossiles. 331 



of the work ; it will be sufficient to point out the principal 

 modifications of the general type, and to afford a few exam- 

 ples of their secondary variations. 



Some genera of fishes have no scales whatever, nor even 

 parts analogous; the epidermis in that case rests immedi- 

 ately on the layer of pigment which colours the skin ; such 

 are the Myxines, the Pteromyzons, etc. In the greater part 

 of these fishes, however, the scales are more or less develop- 

 ed, and their position, their form, their consistence, and the 

 nature of their surface varies to an infinite degree. They 

 are contained in the mucous cavities, or little pouches, 

 formed by the corion, to which they are not however 

 attached by vessels. Supported in their position by a 

 duplication of the epidermis, which embraces their pos- 

 terior border, they are formed of plates, or horny or 

 calcareous leaves, superimposed one upon another, and 

 which are secreted from the surface of the corion ; these 

 leaves are each successively attached to the surface of 

 the preceding leaves to which they are united by hardened 

 mucous. To form a just idea of their development, it is 

 necessary to examine them first in those genera of fishes in 

 which the scales are disposed in the most simple state ; for 

 example, in the Eels, the Blennies, the Loaches, and the 

 Leuciscs. These fishes are remarkable for the cells of the 

 corion in which the scales are found ; the anterior border, 

 (that which in other cases is usually imbricated,) is free 

 and unattached to the adjoining part of the cellule of the 

 scale, its posterior border, on the contrary, is contained in 

 a fold of the epiderm which covers the outer surface of each 

 scale, and which, passing by the posterior border of the in- 

 ternal surface, a part of which it also covers, is continued to 

 the external surface of the following scale, and thus forms 

 the beds of the corion in which the scales are supported, as 

 may be seen in figure 8, t. xi. 



Thus the posterior border of each scale is fixed in a fold 



