374 FISHES. 



As for the rest, whatever opinion may be formed respecting its 

 uses, it is difficult to explain how an organ so considerable has been 

 denied to so great a number of fishes, and not only to those which 

 generally remain quiet at the bottom of the water, as the rays and 



the pharynx oi - the stomach by means of ainembranous canal. Many blood vessels, as 

 ■well as the branches of the pneumogastric and great sympathetic (l) nerves are dis- 

 tributed through its sides. The air it contains is composed, according to the re- 

 searches of Priestley (2), Fourcroy (3), Brodbelt (4), Bict (5), Erman (6), Con- 

 figliachi (7), Provencal and Humboldt (8), Geoflroy (9), and Delaroche (10), of the 

 same elements as the air, that is, of oxygen, azote, and carbonic acid ; but their 

 proportions are subject to great variation. Erman has found, in fresh water, fishes 

 less of oxygen than there is in atmospheric air, whilst, according to Bict, the pro- 

 portion of this same gas is more considerable in sea-fish, especially those which keep 

 at a great depth. Lac^pede (l) pretended that he has" also found in it hydrogen, 

 but no other naturalist agrees with him on this assertion. 



Very probably the natatory bladder performs the part of an accessory organ in 

 respiration, as Fischer (2), Nitzocb (3), G. R. Treviranus (4), and many others have 

 admitted. The fishes which are remarkable for their very quick and prolonged move- 

 ments, appear to be principally those whose respiration is carried on by the assistance 

 of this organ. They appear to accumulate the respirable air in those circumstances 

 in which they take in more than they can consume, and employ this reserve in other 

 circumstances in which they have need of a greater quantity of air. And what seems 

 to favour this hypothesis, is that flying fish, such as the mullets, and according to 

 the researches of Humboldt, the flying fish are furnished with very ample natatory 

 bladders. Delaroche has also seen this organ very large in the flying scorpcena, 

 whilst those species of the same genera which do not fly (scorpcena, porcus, serofa, 

 dactyloptera, &c.) ; are generally without it. A volumious natatory bladder is 

 likewise found in the salmons, the sword-fishes, the pike, the herring, &c, which are 

 distinguished for the rapidity of their progress, whilst it is not so in those fishes 

 accustomed to remain at the bottom of the waters or in the mud, and whose move- 

 ments are slow, as the rays, the lampreys, many blennies, the remora, the bull 

 heads, &c. 



It is still doubtful whether this bladder ought to be considered as acting simul- 

 taneously as an organ vicarious to the process of natation, and allowing, by its dis- 

 tention or contraction, the fishes to raise or to sink themselves into the water, as is 

 the opinion of Borelli. As many fishes deprived of it are nevertheless good swim- 

 mers, as in others it does not always communicate with the pharynx and stomach by 

 means of a canal which allows the air to pass out of it ; and in fine, as it is sometimes, 

 as in the loche cobites fossilis, for example, enclosed in an osseous capsule, which 

 consequently does not allow it to dilate or shrink : this opinion does not appear very 

 plausible. It may again be alleged that fishes in which the natatory bladders has 

 been burst, still retain the faculty of rising and descending in the water, as the ex- 

 periments of Humboldt and Provengal have incontestably proved. 



Many fish breathe also by the intestinal canal, by means of the air which they 

 swallow. This fact Erman has demonstrated in his beautiful experiments on the 

 cobites fossilis. The air escapes at the anus in the state of carbonic acid gas. The 

 electric eel rises also to the surface of the water, according to the observations of 

 Humboldt, in order to take in the air. 



Sylvester has also shown that fishes which thrust themselves into the mud occa- 

 sionally, rise to the surface of the water for the purpose of obtaining the air mixed 

 with it, the air which they had in the water below being wholly consumed by 

 respiration. 



The results of the experiments by Dr. Edwards, of Paris, prove that the necessity 

 of respiration is increased in fishes by increase of temperature, so that during sum- 

 mer very many fishes are obliged to draw in air by the mouth. 



Such are the facts recorded by this author, and it only remains for us to refer the 

 reader to the very curious and interesting experiments of Dr. Edwards, to which 

 M. Tiedmann has just alluded, and of which an account will be found in the preced- 

 ing Section on Respiration. — Eng. Ed. 



