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frequent the bottom, have a low degree of respiration, great muscular irrita- 

 bility, less necessity for oxygen, live long out of water, and the flesh not so soon 

 subject to decomposition. Thus is each peculiarly adapted to its general abiding 

 place ; for, I need scarcely say, it is a mere vulgar error to suppose that fishes breathe 

 water. Their life is sustained by air as well as our own. The water taken in, 

 either by the mouth, or by an apparatus fitted for the purpose, in passing through 

 the fihuueuts of the gills, imparts to these the oxygen of the air it contains ; re- 

 ceiving carbon in return ; precisely like any of what are popularly considered air- 

 lireathing animals. The water, in its passage through the gills, is not decomposed ; 

 but merely the oxygen extracted from the atmospheric air contained in the water. 

 Deprive water of this air, and no fish can live in it. Now as — especially in cold 

 weather — the ground fish are partially, and often wholly, buried in sand or mud, 

 their low degree of respiration is perhaps necessary to existence ; as in such a 

 situation they must obtain a more limited supply of air, than in the free and 

 open water ; thus, not very remotely, approximating to the hybernating animals 

 of earth. 



I must close these slight remarks on the Ichthyology of Herefordshire, by 

 adverting to one part of the economy of fishes, which remains unexplained — at 

 least satisfactorily — the air-bladder. Its office is usually supposed to be that of 

 enabling the fish to raise or depress itself in the water, at will, by a sudden 

 and voluntary alteration of its own specific gravity. But this may reasonably be 

 doubted ; for at least one fourth of the race are without it. Were this large 

 proportion condemned to crawl at the bottom, we might have better reason to 

 believe the air-bladder necessary to empower the fish to rise. It is not so, how- 

 ever. The cartilaginous tribes are deprived of it ; and we have a familiar 

 instance in our two species of mackerel — ^both having bony skeletons ; and both 

 possessed of precisely similar habits ;— yet the one has an air-bladder, and the 

 other has not. If the air-bladder enable the animal to rise and sink, at pleasure, 

 it is clear that the one without such organ, and which can yet perform the same 

 office, must either have some compensating power, hitherto undetected, or the 

 air-bladder is not necessary for the purpose to which it is commonly presumed 

 applicable. No scrutiny has been able to discover any equivalent in those genera 

 which have it not : and it would seem, at least, very anomalous, to be requisite 

 in the progression of one and not of another, unless the structural difference were 

 far more considerable than it is found to be, in many instances. Chemical analysis 

 has proved that the air contained in these bladders is not atmosplieric air ; nor is 

 it universally the same in all fishes — nitrogen being in excess in some species, and 

 oxygen in others ; which would lead to the deduction, that it was not a mere 

 swimming apparatus ; for they are filled with an animal fluid ; and I am not 

 aware that in any branch of physiology a natural secretion is elaborated, except 

 in connexion with some vital function ; which the simply moving upward, or 

 downward, in the water, cannot be considered. We must, therefore, look for some 

 faculty in those to whom has been granted this additional organ, which is not 

 held in common with such as are deprived of it : for, in all animate nature, where 

 the organism is varied, so I believe, arc the demonstrations. 



