234 HENRY C. TRACY 



The physiological problem is even more complicated when 

 it is a question of the function of these two organs, brought 

 into relation to each other by a definite mechanism. Is one 

 organ accessory to the other, and, if so, which of the several 

 functions of one organ does the other subserve? Or, is some 

 entirely new function evolved as the result of their interrelation 

 by the development of a connecting mechanism? 



Most of the anatomical papers on the ear-swimbladder rela- 

 tion offer suggestions and sometimes extended discussions on 

 the physiology of the mechanism, but it seems remarkable that 

 in a century since Weber no experimental work on this unique 

 relation has been recorded. The theories suggested cannot be 

 discussed here in detail, but the most important of them may be 

 summarized as follows: 1) accessory to hearing (Weber); 2) 

 perception of hydrostatic pressures (Hasse); 3) appreciation of 

 changes in barometric pressures (Sagemahl). Bridge and 

 Haddon ('93), in an important paper on the Weberian ossicles, 

 have shown that the anatomical structure of this mechanism is 

 not consistent with the first or third theory, but is adapted to 

 perception of changes in hydrostatic pressures. Wright ('84) 

 came to the same conclusion. 



With regard to the physiology of the Clupeoid type of the 

 ear-swimbladder relation, little has been written. At the pres- 

 ent time, however, the anatomical relations of these structures 

 are perhaps sufficiently well known to justify the statement of a 

 physiological theory, which it is to be hoped may be confirmed 

 or modified later by experimental work. 2 



- The lateral recess of the skull would appear to furnish an easy means of 

 reaching the ear-swimbladder mechanism in Clupeoids in experimental work 

 (fig. 12). This recess is separated from the outside only by the lateral wing of 

 the frontal bone which is quite superficial. The Clupeoids, however, or at least 

 t he American species, seem in general unfavorable for physiological experimenta- 

 tion. They are free-swimming in their habit and hence do not thrive when con- 

 fined in small enclosures. They are delicate and of a 'nervous temperament,' 

 so to speak, and they do nol easily adjust themselves to handling and to opera- 

 tive procedures. Fishes with the Weberian ossicles, e.g., siluroids and certain 

 cyprinoids, would appear to be much more favorable for experimental study of 

 the ear-swimbladder relation. 



