on th^ Air-hladder of Fishes. 301 



the air, which would be no longer con)pressecl, would be 

 loo iiJuch dilated, and would render the fish too light, or 

 even produce some rupture, as happens to fishes drawjv 

 buddcnly from great depths. or; 



But who is there who is not aware, that tliis, on the part 

 oF nature, would he eorrccliui!; very chunsily a detect which' 

 she nnghi have retrained from introducing at all iuto her 

 work ? She had only to give no air bladder-at all to fishes; 

 and we have seen that she need not have done so to place 

 them in equilibrium with the water: in that case she would, 

 no longer have required the apparatus ot compression,! 

 which has been supposed as serving only to cprrpiCt tj^e Uii"" 

 convenience of an useless bladder. i ,. xf St 



. Thus we are of opinion that the third, and the chief 

 part of the commonly received opinion, in reality resolves 

 the problem : we mean that part of it which says, that the 

 biadtler is placed there to assist the fish in ascending and de- 

 scendmg, according as it is compressed and dilated; and 

 we confess that we do not see why M. Delaroche should 

 reject this use of the bladder, to which the two others are, 

 in our opinion, merely accessaries. ? • fj r^ 



That the fish has strength sufficient to enable it to de- 

 scend, clearly results from what M. Delaroche himself ad- 

 mits ; for if the fish, which ascends 30 feet for example 

 (and it ig difficult not to believe that many fishes can 

 ascend that height without any accident), if, we say, such a 

 fish has sufficient strength to compress its bladder, by means 

 of its muscles, to the same degree that the 30 feet of 

 water formerly did, it is evident that a similar fish, sup- 

 posed,to be in equilibrium at tlie height to which the former 

 ascended, will also have suffi'cient strength to compress its 

 bladder, as nmch as would the addition of a weight of 30 

 feet, and that there would result from such a compression 

 or diminution of volume more than sufficient to force it to 

 descend. 



M. Delaroche, against this most essential part of the vul- 

 gar opinion, advances only a single objection, which he 

 borrows from M. Fischer : this is, that the variation of spe- 

 cific gravity which may result, with respect to the total 

 body of fishes, from the variations of the volume of the 

 bladder being very small, the ascents or descents, which 

 are 1 he consequence of it, could not but be very slow: 

 but, besides, the circumstance of these variations never 

 having been yet measured, no person has ever said that 

 the bladder caunot be aided in this function by other or- 

 gans. Those fishes which have no bladder, ascend and 



descend 



