486 



Covtparative Animal Physiology 



In fishes of the suborder Ostariophysina (carps, catfishes, characins, and 

 gymnotids) the lagena is large and contains a very large statolith. In the non- 

 Ostariophysina both the lagena and the statolith are smaller. The statoliths 

 of the sacculus, utriculus, and lagena of both the Ostariophysina and non- 

 Ostariophysina are attached loosely by two marginal membranes to the wall 

 of the vesicle in such a way that they are free to vibrate. As they vibrate they 

 make contact with the sensory epithelium. This relationship is shown in 

 Figure 162. 



Fig. 163. The coupling between the air bladder and the labyrinth by means of Weber's 

 ossicles in the Ostariophysina. Weber's ossicles, black. Redrawn from v. Frisch." 



In the Ostariophysina hearing is very acute, and the air bladder is con- 

 nected to the auditory organ, particularly to the sacculus, by a chain of bones, 

 the Weberian ossicles (Fig. 163). This bony connection makes it possible 

 for the air bladder to function as a hydrophone which picks up pressure waves 

 over a wide surface of the body wall and transmits them to the ear by means 

 of the ossicles. These ossicles are homologous to the bones of the mammalian 

 middle ear, but are embedded in tissue rather than suspended in the air, as 

 in mammals. The saccular statolith is especially modified for the reception 

 of sound waves directed toward it by this bony mechanism, which is responsi- 

 ble for the high sensitivity of these fishes. 



That the lateral line organs of fishes participate in reception of low-fre- 

 quency sound waves has been demonstrated by Parker and Van Heusen^- 

 and Hoagland--. Parker and Van Heusen showed that the lateral line organs 

 of catfish are stimulated by sonic vibrations up to 344 cycles per second, as 

 evidenced by absence of the response of the fish to auditory stimuli in the 



