Zbc air BIa^bcr of jf iebce con0it)cre^ as a 

 Degenerate Xung. 



By Mrs. Alice Bodington. 



the result of numerous investigations as to the 

 condition of the air-bladder of fishes, Mr. Charles 

 Morris, of the Academy of Natural Sciences of 

 Philadelphia, has arrived at the conclusion that 

 this organ was not primarily evolved as an aid in 

 swimming, but was originally a lung. 



As with most degenerating organs, the air- 

 bladder is found in all stages of arrested develop- 

 ment. In the most highly-specialised fish, the 

 Teleosteans, it exhibits an extraordinary variation in shape, size, 

 and relation to the body. With some Teleosteans the air-bladder 

 has an open pneumatic duct connecting with the oesophagus, and in 

 a few cases with the stomach. With others this duct exists, but its 

 cavity is closed. In some cases it is reduced to a fine ligament. 

 In many other Teleosteans no traces of it exist. T/iese variafiofu 

 have no appreciable effect upo?i the velocity and activity of the fish. 

 Those that have no air-bladder seem in no respect at a disadvan- 

 tage as compared with those that have one. These variations 

 remind one of the various stages of degeneration of the eye and 

 optic nerves in blind animals. 



If the air-bladder is of absolute necessity to a fish as a gravi- 

 tating organ, why is it not necessary to all, and why has it not 

 developed into some shape and condition of greatest efificiency ? 

 No animal organ, whose function is of known importance, presents 

 such extraordinary modifications. In the heart, lungs, brain, etc., 

 there is one shape, position, and condition of greatest efficiency, 

 and throughout the lower forms we find a steady advance towards 

 this condition. There is in all these organs a persistent movement 

 towards homogeneity — not towards heterogeneity, such as we find 

 in the air-bladder. The existence of the air-bladder is proof that 

 it has had, at some time, a function of considerable importance. 

 Its many variations go to prove that it has ceased to perform any 



New Series. Vol. I. 



1888. P 



