3"2 FI8HK8. 



Tlie cellular tissue placed under the skin, is more or less filled with 

 an oily grease : it is abundant in the genera of salmons, and in some 

 other fishes noted for being fat; but this is not the greatest number. 

 In some, as the moon-fish, there is a thick layer of a kind of bacon ; 

 but gelatinous and not oily. 



An oily grease fills also, very generally, the interval between the 

 muscles, and we have seen that it is almost always round the brain. 



Some fishes, nevertheless, want this grease; the cod, the pluronectes, 

 and. in general, the cartilaginous fishes have it not even in the cra- 

 nium ; the sturgeon on the contrary, lias this grease, which surrounds 

 the brain very abundant and very compact. 



One of the most rem irkable secretions which take place in the 

 body of fishes, is that of the air which fills their natatory bladder; at 

 least it is pretty certainthat, in the very numerous genera in which this 

 bladder has no external communication, the air, which it contains, can 

 only be produced by a secretion, for which purpose there is an addition 

 in these genera of very diversified glandular organs*. There also 

 exist fishes, such as the eel, which combine a canal of communication 

 with the glandular organs ; but in the greatest part of those which 

 have this canal, we do not see the glands. 



The bladder itself is composed of a tunic, extremely fine internally, 

 and of another tunic which is thicker ; itisalsoof a verypcculiarfibrous 

 nature, and which yields the best isinglass; it is lined externally 

 by the general tunic, which the peritonium affords to all the intes- 

 tines. It is sometimes simple, as in the perch ; sometimes furnished, 

 as in certain cod, with appendices more or less numerous, and some- 

 times branched, as in certain scicenas ; sometimes it is divided into two 

 parts, one anterior and the other posterior, by a strangulation, as in 

 the cyprins, the myripristis, the therapons, and many of the salmons, 

 or into two lateral parts by an emargination, as in the tetrodons and 

 the diodons. The catcstomes have it divided into three parts. . It is 

 principally in the abdominal fishes that it communicates by a pipe 

 with the intestinal canal, cither with the oesophagus as in the cyprins, 

 or with the I ottom of the stomach as in the herrings. That of the 

 sturgeon is immediately directed into the oesophagus by a large 

 opening. It is sometimes furnished with muscles proper to itself, es- 

 pecially in the scioena, and in several salmons of the division of charax, 

 (the sargus of the author.) 



It is generally azote, mixed with seme fractional parts of oxygen 

 or caibcnic acid, which is found in the natatory liladderf. 



Nevertheless, M. Configliacchi asserts that he has found there as 

 much as forty centimes of oxygen ; M. Biot has remarked that those 

 fishes which are accustomed to live in deep water, have this gas in a 



* Gauthier Needbam, in his treatise De format o fceto, is the first who cave par- 

 ticular attention to this organ, and who established the fact that the air is intro- 

 duced into it by secretion. Redi in his Observations on Animals that feed on 

 living animals, has settled the precise bo lies which are employed in several fishes for 

 this secretion; Kalfceuter has also given proofs of this origin in his memoir on the 

 late, Nov. Coinm. petrop., vol. xix. My Memoir on the Maigre as respects the same 

 subject is in the Mem du Mus., vol. I., p. i. 



t This observation is dull : originally to Fourcroy. 



