FISHES. 



349 



Fatty matter formed chiefly of oleine 



Azotic matter 



Chloruret of sodium 



Subcarbonate of soda 



Sulphate of soda 



Subcarbonate of lime 



Phosphate of lime (of bones) 



Phosphate of magnesia 



Peroxide of iron 



Loss 



In a considerable number of genera, the scales are imbricated : that 

 is to say, they partially cover each other like tiles ; their external and 

 apparent part is merely covered by a lamina of the dermis, which very 

 speedily dries ; their concealed part, is buried in a cavity, or purse 

 hollowed out of the dermis or formed by one of its folds ;* this con- 

 cealed part of the shell, has usually a different surface. AVe perceive 

 on it, very fine strite parallel with its edge, and rays spreading like a 

 fan from the centre towards the edge, which is most frequently cut 

 into lobes and indentations. The uncovered part presents more 

 variety ; it is sometimes smooth, sometimes pointed, sometimes 

 covered with little asperities, or cilise. The scale thus enchased 

 in the dermis, does not adhere to it by vessels.f but it would appear 

 that it grew like the shell in the mantle of a mollusca,or as a tooth in 

 its germ and its matrix, and the varities of the surface of the scales, 

 their furrows, their dimples, their crests, the spines of which are 

 armed or bristled, the lashes or small notches of their edge, and 

 which give, when viewed through the microscope a very agreeable 

 sight,! d° not sul 'P ass what is seen in shells, and in these nobody 

 doubts that the growth is by layers. 



* It might be thought at first sight, that this disposition was very different from 

 that which obtains in a great number of lizards and serpents, in which what is called 

 scales, is merely a production of the dermis, covered by the epidermis, which assumes 

 at its external surface more thickness and consistence ; but the sauriaris conduct us to 

 the tiled scales of fishes : the folds of their skin are occupied by a calcarious secre- 

 tion, which forms a true scale plainly separable from the substance of the derm 

 which envelopes it. Let is suppose this substance of the derm thinner and finer, 

 and we shall have the scales of fishes, which seemed to be enshrined in a fossa of this 

 dermis. 



•f- Leuwenhoek was the first to assert that the scales grew by layers which were 

 successively larger, and which were formed under the preceeding ones. (See his 

 works, page 205 ; his physiological epistles 214.) But^he erroneously believed that 

 the years of the age of the fish could be distinguished by the layers in the scales. 



X The figures maybe seen in Baster (opera subseciva I, III, pi. 15) and in some 

 plates of Amusements microscopiques of Ledermuller. Schcefer gives also figures of 

 the scales in Pise, Bavar and Pentas, and some are also to be seen in other Ichthy- 

 ologists. I do not find that Broussonnet in his Memoire, inserted in the Journal de 

 Physique, t. XXXI, p. 12, has added much to the reports of his predecessors. 



