EAR-SWIMBLADDER RELATION IN CLUPEOIDS 239 



precoelomic diverticulum; smooth muscle surrounds the open- 

 ing of the diverticulum to the body of the swimbladder and is 

 also found in the walls of the pneumatic duct which opens into 

 the stomach. Apparently, therefore, a mechanism for the ad- 

 justment of the gas pressure in the swimbladder exists; the 

 nerve impulses controlling it are doubtless of a reflex nature and, 

 in the absence of experimental evidence to the contrary, it seems 

 a reasonable hypothesis that the source of the afferent impulses 

 of this reflex is in the divisions of the macula recessus utriculi. 



That this mechanism is effective in maintaining the fish at a 

 nearly constant level is scarcely consistent with what little is 

 known regarding the habits of these fishes. 



It is known that herring and menhaden, within a few minutes, 

 will dive below the surface to depths greater than the bottom of 

 the purse seines of the fishermen. Possibly, however, while 

 this mechanism may not suffice to force the fish to remain 

 near one level, it may by compensatory motions of fins and body 

 musculature tend to prevent the fish from departing far from a 

 certain level except in extreme cases. 



This apparatus, however, may be effective in maintaining 

 the fish at certain water levels within certain wide limits. The 

 mechanism of secretion and absorption of gas in the body of 

 the swimbladder probably has its physiological limits; it is 

 possible that the mechanism described may prevent the fish 

 from descending to depths greater than those at which the fish 

 is able to adjust the gas pressure in the body of the swim- 

 bladder to the hydrostatic pressure. 



Anatomical work, however, can hardly go further than the 

 statement of the problem and the discussion of its possibilities. 

 Further analysis of the function of this mechanism can only be 

 attained by experimental work. 



