10 NATURALIST'S CABINET. 



* 



Opinion of ancient philosophers. 



its expansion. The carp continued to live on 

 being thrown into water, but was unable after- 

 wards to rise to the top. The same circum- 

 stances are consequent upon any prick or wound 

 of the bladder by which the air may escape ; for 

 in such cases the fish continues to crawl at the 

 bottom. And such animals as river cray-fish, 

 oysters, lobsters, crabs, 8tc. that never quit the 

 bottom of the water, are found destitute of any 

 air-bladder. 



Ancient philosophers have in general enter- 

 tained an opinion, that this vesicle does not 

 merely serve for the purpose of varying the spe- 

 cific gravity of fish, but for some purposes essen- 

 tially necessary to life. Dr. Priestley also con- 

 jectures, that they may serve some other inten- 

 tions in the animal economy, besides that of the 

 raising or depressing of the fish. 



The most conclusive of the several argu- 

 ments on this side the question is, that all the 

 cartilaginous kind of fish want air-bladders, and 

 yet they rise to the top, or sink to the bottom 

 without any difficulty; and also, that though 

 most of the eel-kind have air-bladders yet they 

 cannot raise themselves in the water without 

 great difficulty. 



Some interesting facts relative to this subject 

 of the air or swimming-bladder, have been com- 

 municated by Dr. Munro. This gentleman says 

 " It has long been known that in the flat fish 

 there is no swimming-bladder and in a few long- 



