Recherches sur les Poissons Fossiles. 



519 



sometimes triangular, square, pentangular, or having the two 

 sides insymmetrical, that is flat on one flank and arched on 

 the other, and with the bones of the head so much dispro- 

 portioned, that the two eyes are turned to one side of the 

 animal,* (as the Soles, &c.) 



The essential character of the skin is to envelope com- 

 pletely the animal, and to form thus a sort of external skele- 

 ton for the protection of the surface, as the osseous skeleton 

 protects surrounding internal organs. 



In the invertebrated animals, there are no other solid sup- 

 ports than those which are produced by the integuments, or 

 which depend on them; nevertheless, we would be wrong if 

 from that circumstance we were to draw a parallelism with the 

 osseous skeleton of the vertebrated animals, which is ex- 

 clusively peculiar to these last, and which has no point of 

 analogy with the solid pieces of the inferior classes. They are 

 much more the productions of the skin, that, m the ver- 

 tebrata represent the skeleton of the invertebrata ; and yet 

 we can trace completely the parallism of different degrees of 

 progression in the Animal Kingdom, notwithstanding the 

 considerable differences in the manifestation of analogous 

 parts between the superior and inferior animals. For we 

 observe even more striking differences between the various 

 productions of the skin in vertebrate animals than that which 

 we have just remarked in the invertebrate. As to the rest, 

 it is enough to know, that these metamorphoses of the skin 

 have a peculiar tendency to the surface of the body, and pre- 

 sent constant relations between the skin and other systems 

 of organs. However, the skin is not intended alone for the 

 external surface of the body, it penetrates also into the inter- 

 nal cavities which it lines, and on the surface of which, it 

 produces equally the solid parts of different structures, to 



* Several examples of this form are presented by the fishes of India ; 

 they are familiar to the fishermen of Bengal under various names, 

 as Pan, Arsee, Nauphala, &c. — Ed. 



