eM jad o 
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 Amiwrus 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 reopening 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 Anzerger cited above, 
I have remarked that the parts concerned in Amiwrus indicate a much 
further specialization of the condition in the Cyprinoids. I propose, 
in a future paper, to investigate the alterations which the anterior 
vertebree have undergone in other sub-families of Silurvids, for the 
researches of Reissner (Miiller’s Archiv, 1868), and those of Miller 
himself, (same journal, 1842) indicate that these must depart very 
widely from the condition found in Am/urus. 
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 vertebra became 
modified in connection with the air-bladder. 
