Recherches sur les Poissons Fossiles. 321 



As to the development of the skin, it is at first seen to be a 

 mere serous film of the blastoderme, or first rudiment of 

 the common envelope of the body. In the mean time, the 

 observations which have been recently made on the ad- 

 vanced period of development of the egg, promise soon 

 to prove the serous membrane to be the common basis 

 from which the bones, the muscles, and the skin are equally 

 formed. This is separated again into many lamina, amongst 

 which are distinguished, first the epidermis, afterwards we 

 see the formation of the net of malpighi, the corion, and 

 the subjacent muscular coat. 



In the fishes, the skin is always much more tense at 

 the surface of the body than in other animals; uniting to 

 the muscles by a dense cellular tissue, and is never possess- 

 ed of so much mobility as in other vertebrated animals. In 

 the class we are now speaking of, it is the corion and 

 the solid parts produced at the surface of the malpighien 

 net, that acquires such considerable development under the 

 term of scales. But in order, to afford an accurate idea of 

 the structure of scales, which is to form the principal question 

 for our consideration in this chapter, it is indispensable to 

 know the condition of the different layers which are formed 

 in the integuments of those animals in which the skin is most 

 organised. 



First the epidermis^ the outermost part of the skin, may 

 be regarded in a general point of view as a membraneous 

 lamina of horny substance, which covers the whole surface of 

 the animal, isolates it from the external world, defends the 

 parts of most delicate organization, and which as a bad 

 conductor of heat, preserves to the animal that proportion 

 of warmth which is proper to it. The epidermis is insensi- 

 ble, and is reproduced readily ; it is composed of a great num- 

 ber of layers or folds, superimposed and strongly adherent 

 to one another. It is the modifications of the folds of 

 the skin, that is to say, the hair, the feathers, the scales, 



2 T 



