80 F. G. HALL 



Among the important functions assigned to the swimbladder 

 are: (i) phonation, or sound producing; (2) respiration; (3) 

 accessory audition; (4) hydrostatic activities. 



The respiratory function is believed by most scientists to be 

 important only in a few species. The sound-producing function 

 also has been demonstrated in a limited number of species. 

 Apart from the function of phonation, the swimbladder occasion- 

 ally becomes subservient to the auditory organ, with which it 

 may be connected directly or through the interpolation of 

 certain modified parts of the anterior vertebrae. The most 

 important function of the swimbladder is hydrostatic, by virtue 

 of which a fish possesed of such an organ is able to alter the 

 amount of contained air and consequently its own specific 

 gravity, so as to be in equilibrium with the surrounding medium 

 under varying pressures. 



The investigations to be described in this paper began during 

 the summer of 1921 while the author was in the employ of the 

 United States Bureau of Fisheries. From results obtained that 

 summer and from suggestions gained from Dr. A. S. Pearse, it 

 was thought worth while to continue the study of the functions 

 of the swimbladder. Pearse (1920) had previously shown that 

 the swimbladder gases change in percentage, oxygen becoming 

 less, when perch are kept in water containing small amounts of 

 dissolved oxygen. An attempt was first made to ascertain 

 how important this fact might be in explaining how fishes are 

 able to go into regions where the oxygen is extremely low or 

 entirely absent and live for several hours. The problem devel- 

 oped from that work and was finally extended to cover other 

 functions which the swimbladder might perform. The experi- 

 ments were restricted to yellow perch, Percaflavescens (Mitchell) ; 

 large mouth black bass, Micropterus salmoides (Lacepede) ; and 

 carp, Cyprinus carpio (Linnaeus) ; A few comparisons were 

 made with other species inhabiting Lake Mendota. 



HISTORICAL. 



The role that the swimbladder plays in the life of fishes has 

 attracted the attention of investigators for a long time. Aristotle 

 believed the organ to function chiefly in the production of sounds. 

 Borelli ( 1 680) was perhaps the first to attribute to the swimbladder 



