386 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



in equilibrium, and the recording apparatus connecting the air-bladder 

 with the auditory organ, when present, probably enables them to meas- 

 ure the precise amount of air, which must be disengaged in order to 

 restore equilibrium at a new higher level. The mode in which air is 

 discharged in Amiurus is not known to me, but the duct, tortuous 

 where it opens into the oesophagus, must be much straighter when 

 the ventral wall of the anterior part of the air-bladder is distended 

 than when such is not the case. Further investigation must show 

 whether the duct participates actively in disengaging the air-bubbles, 

 and if so, under control of what nerve it does so. 



The whole physiology of audition in the Teleosts is so obscure that 

 it is worth while i*eopening the question of the possible role of the 

 air-bladder and its accessory ossicles in connection therewith. Amiurus 

 would be admirably adapted for physiological experiment, for it is 

 very readily kept in captivity, and has extraordinary vitality. If 

 the above descriptions serve as an accurate morphological basis for 

 such experiments part of my object will be fulfilled. 



In my note on this subject in the Zoologischer Anzeiger cited above, 

 I have remarked that the parts concerned in Amiurus indicate a much 

 further specialization of the condition in the Cyprinoids. I propose, 

 in a future paper, to investigate the alterations which the anterior 

 vertebrse have undergone in other sub-families of Siluroids, for the 

 researches of Reissner (Midler's Archiv, 1868), and those of Mtiller 

 himself, (same journal, 1842) indicate that these must depart very 

 widely from the condition found in Amiurus. 



It is among the Cyprinoids, nevertheless, that a less altered and 

 more primitive condition of affairs must be sought, and it is possible 

 that an extension of research, anatomical and developmental, may 

 explain the steps by which parts of the anterior vertebrse became 

 mollified in connection with the air-bladder. 



