229 
The example figured is 11:2 inches in length, and was 
procured by Dr. Lomsz, of Torquay, for the Rev. W. Symonps, 
of Pendock, who kindly sent it to me, and subsequently a black 
spotted male from the same source. Inside the stomach of the 
figured fish was an almost entire Loach, Nemucheilus barbatulus, 
2°5 inches in length. 
I observed that the Burbot possesses an air-bladder, which is 
of the Physoclisti type, and destitute of any chain of ossicles 
connecting it with the internal ear, and I propose offering some 
general remarks upon the situation and functions of this organ 
as commonly observed. The uses of the air- or swim-bladder, 
likewise termed the air-sac or air-vessel, have long been subjects 
of speculation and formed material for discussion. It is a 
single or variously sub-divided sac, or it may be two sacs, 
partially or completely separated one from the other. Situated 
above the centre of gravity,* it lies beneath the vertebral 
column or back-bone, from which it is more or less divided by 
the kidneys, while inferiorly it is separated from the intestines 
by the peritoneum. As the air-bladder is entirely absent, or 
ceases to be developed in many fishes, and is frequently present 
or wanting in species belonging to the same genus, it would 
appear that it is not indispensable to their existence, its 
functions being accessory or supplemental, under certain con- 
ditions, to those of other organs of the body. 
Investigating the origin of this organ in the embryonic 
stage, we find it originating as a bud or offshoot from the 
upper portion of the alimentary canal, or even from the 
stomach ; this offshoot elongates into a blind tube, and then 
enlarges at its terminal extremity into what will eventually 
form the air-bladder. Consequently at some period of a fishes 
existence there must be a tube connecting the air-bladder 
(when one exists) with the alimentary canal, into which it 
* Were the air-bladder below the centre of gravity, or its contents evacu- 
ated into the abdominal cavity, the fish (unless its fins were very greatly 
developed) would roll over on its back, as we see occurs in Tetrodons and 
Divdons, when they inflate their large cesophageal sac, 
