'Sflf6 Report on a Memoir of M. Delaroche, 



necessary to guide us in forming an opinion of his theory, 

 we think it right to say a few words upon two memoirs pub- 

 lished since. 



One of these, by M. GeoflTroy, refers to an earlier memoir, 

 in which he develops, anatomical! v, the means by which 

 the fish compresses or relaxes its bladder, in order to descend 

 or ascend. Indeed, he says at the same time, in the intro- 

 duction of'^his memoir, that the bladder is bv no means an 

 organ of motion by itself; but this is because he thought 

 that those who regarded it as such, suppose that it is dilated 

 by the increase of the air which it contains, and vice versa, 

 an opinion which no person seems to have entertained ; for it 

 is always by the action of the muscles that it has been made 

 to be compressed or dilated : on this subject, therefore, 

 M . GeoflTroy is really of the opinion of Borelli, which is 

 the commonly received idea. 



. The other memoir to which we have alluded, is by Messrs. 

 Humboldt and Provencal, and has for its chief object the 

 respiration of fishes ; but these authors have naturally been 

 led to examine the air in the swinnning-bladder. 



They operated upon river fishes, and found the fax vari- 

 able in composition from 99*0 of azote to 87*0. They have 

 observed as much as 5*o of carbonic acid. They made 

 some tench respire hydrogen, and yet their air-bladders 

 when examined exhibited none; by keeping them in oxygen, 

 however, the proportion of the oxygen in the bladder was 

 somewhat increased. On removing the bladder fron) them, 

 thev were not prevented from producing by their respiration 

 the ordinary eifects upon the atmosphere; they were even 

 able to raise themselves in the water, although they gene- 

 rally remained at the bottom of the vessel. 



Thus, in the numerous works we have analysed, almost 

 every possible hypothesis has been proposed, attacked, or 

 defended, and examples have been given of almost all 

 the combinations of organization that could be devised, 

 M- De-aroche had only therefore to examine these organiza- 

 tions a little further, in order to reduce them to general 

 rules, and to weigh over agam the arguments advanced for 

 or against every hypothesis. 



Let us see how he has acquitted himself of this task. — 



His residence at Ivica, Formentero, and on the coast of 

 jBpain, with Messrs. Biot and Arrago, having furnished 

 bini with opportunities of examining a great number of 

 Mediterranean fishes not to be seen any where else, and 

 their air-l;ladders having chiefly occupied his attention, he 

 ^pptinued his inquiries after his return, on pur common 

 .'■•-'• fresh- 



