110 Profs. T. W. Bridge and A. C. Haddon. [June 16, 



afforded by the almost total absence of any experimental evidence 

 directly bearing on the physiological significance of the Weberian 

 ossicles ; and while we desire to emphasise the danger of deducing 

 function from facts of a purely anatomical nature, no other course 

 has yet been adopted by previous writers on this subject, and at 

 present is the only one open to us ; consequently, any conclusions 

 based upon data so frequently unreliable and misleading must partake 

 rather of the nature of suggestions, and be accepted with considerable 

 reserve. With the qualifications rendered necessary by these con- 

 siderations, some light may possibly be thrown on this difficult 

 problem by a careful inquiry as to how far the Weberian ossicles and 

 the coadapted parts of the air-bladder and auditory organ are 

 anatomically fitted to act as subsidiary or accessory structures in 

 connection with any of the several functions assigned either to the 

 air-bladder or auditory organ, while unsuited for association with 

 others. By this means it may at least be possible to eliminate certain 

 functions from any further consideration, and thereby considerably 

 narrow the scope of future inquiry. 



With this object we propose to discuss (I) how far the function of 

 the Weberian mechanism is conditioned by the anatomical structure 

 of the air-bladder and auditory organ, as well as by the character of 

 the mechanism itself; (II) to which of the known functions of the 

 air-bladder and auditory organ the Weberian ossicles are to be re- 

 garded as accessory structures ; and (III) the utility of the mechanism 

 to the Fish possessing it. 



I. In all the Siluridee normales the air-bladder may be regarded as 

 consisting of two intercommunicating but physiologically distinct 

 portions a posterior, represented by the two lateral compartments, 

 which is indistensible and inelastic, aind always of greater internal 

 capacity, and an anterior, which is always more or less elastic 

 and expansible, but of less internal capacity than the former. 

 The distensibility of the anterior chamber is, however, by no 

 means uniform in all directions ; on the contrary, the peculiar 

 construction of the chamber and its intimate relations and con- 

 nections with neighbouring skeletal structures render it absolutely 

 inexpansible except laterally, that is, in a direction at right angles 

 to its antero-posterior axis ; and from the mode in which the 

 fibres forming the lateral walls of the chamber converge in the 

 dorsal wall, and become inserted into the crescentic processes of the 

 tripodes, it becomes still more obvious that it is only by inward or 

 outward bulgings of the lateral walls that variations in the internal 

 condition of the air-bladder are able to set the Weberian ossicles in 

 motion. It is scarcely necessary to point out that by this restriction 

 of the expansion or contraction of the anterior chamber to movements 

 of its lateral walls, the Weberian ossicles are rendered more suscep- 



