THE FUNCTIONS OF THE SWIMBLADDER 



OF FISHES. 



F. G. HALL. 

 ZOOLOGICAL LABORATORY, UNIVERSITY OF WISCONSIN. 



CONTENTS. 



Page 



I. Introduction 79 



II. Historical 80 



III. Experimental Study of Gases in Swimbladder 83 



General Methods 83 



Normal Composition 84 



Effects of Oxygen Deficiency in Surrounding Medium 87 



Effects of Pressure 91 



Effects of Increased Carbon Dioxide 9 2 



Secretion or Diffusion 98 



IV. Discussion 104 



V. Summary 114 



VI. Bibliography US 



INTRODUCTION. 



The swimbladder, or air-bladder, of a fish is situated dorsal 

 to the coelom, between the alimentary canal and the vertebral 

 column. It is a membranous sac containing the atmospheric 

 gases. On a portion of the surface of the bladder there is a 

 vascular and glandular area, known as the rete mirabile, or "gas 

 gland," or "red gland." Embryologically the swimbladder 

 arises as a diverticulum from the dorsal side of the alimentary 

 canal. The primitive connection may be permanently retained 

 as a tubular canal, called the ductus pneumaticus, or it may be 

 entirely absent in the adult. Because of this variation the 

 teleostean fishes have been grouped into two divisions 

 the Physostomi, characterized by the retention of the duct, 

 and the Physoclisti, in which the duct is absent in the adult. 

 In the former group are included the carp, salmon, and eel; in 

 the latter, the cod, bass, and perch. The basis for this distinc- 

 tion between the two groups, however, is far from invariable and 

 many exceptions occur in both. 



The variety of functions performed by the swimbladder is 

 perhaps greater than that of any other organ possessed by fishes. 



79 



