on the Air-lladder of Fishes, 297 



fresh- and salt-wjiter fishes; hence he has furnished upwards 

 of fifty particular descriptions oFthe air-bladders of as njany 

 species of fi«ih, several of which have not hitherto'bccn de- 

 scribed. These descriptions, added to those which former 

 authors had given of" some species which M. Delaroche 

 could not find, form the materials of his present memoir; 

 and he has placed his own at the entl oF the work, as so 

 many proofs of the 2;eneral propositions which he lays down. 



In the body of the memoir he treats successively of the 

 anatomical structure of the air-bladder, of the nature of the 

 sources of the air which it contains, and of the functions 

 which it exercises. 



He speaks in the first place of its existence, and gives 

 a list of those fishes which have it, and oF those in which 

 h is wanting. The result? of this list, which a^lds several 

 species to those which had already been adduced with respect 

 to this subject, are nearly the same which had been alVeady 

 drawn ; namely, that the existence or non-existence of the 

 bladder does not correspond with the other afiinities of or- 

 ganization which connect fishes with each other. 



He afterwards speaks of the various situations of the 

 bladder, (^f its variation in size, and in the configuration 

 of its tunics, (an article in which he compares the internal 

 membrane to the serous membranes) ; and finally, of the 

 particular muscles which it has in several fishes; and he 

 gives a more detailed description of these muscles than is 

 to be found in the comparative anatomy of M. Cuvier. 



What he says on the subject of the canal of communi- 

 cation also presents a great number of novelties. On this 

 head he has made some very acute remarks, and has as- 

 certained that this canal is \Vanting in the greater part oF sea 

 fishes. He did not find it in any of the jugular or thoracic 

 classes, which compose nearly three- fourths of the total 

 species of fishes with which we are acquainted. The lec- 

 tures on comparative anatomy had assigned this canal to the 

 nranoscnpe, which is a jugular ; but according to M. Dela- 

 roche, the authors of' this work have made new inquiries, 

 and found that they were mistaken. 



M. Delaroche has st^tdied in a particular manner the red 

 bodies with which certain bladders are furnished. He found 

 them, like Perrault and Monro, in all those which want the 

 canal of communication, and in the anguilla genus although 

 furnished with this canal. 



Our author gives a very detailed description of these bo. 

 dies, in the gadi, the trigli, the perches, sonie lalri and 

 holocentreSi as well as in the atkerina rhepsetus^ the Henm-us 



physis, 



