372 FISHES. 



The 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 nut oily. 



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

 muscles, and we have seen that it is almost always I'ound 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 contraiy, has this grease, wliich surrounds 

 the brain very abundnit and very compact. 



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

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

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

 bladder has no external commvmication, 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, 

 andof another tunic which is thicker; itisalsoof averypeculiarfibrous 

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

 by the general tvuiic, 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 niunerous, 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 catestomes have it divided into three parts. It is 

 principally in the abdominal fishes that it commiuiicates by a pipe 

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

 or with the Vottom of the stomach as in the herrings. That of the 

 sturgeon is immediately directed into the oesophagus liy a large 

 opening. It is somctiuies 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 some fractional parts of oxygen 

 or carbonic acid, which is found in the natatory bladderf. 



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 NeedUam, in his treatise i)e /o?-;;io/o/ce/o, is the first who gave 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 bodies which are eraploj'ed in several fishes for 

 this secretion. Kalroeuter has also given proofs of this origin in his memoir on the 

 late, Nov. Comm. petrop., vol. xis. My Memoir on the Maigre as respects the same 

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



f This observation is dull : originally to Fonrcroy. 



