134 Proceedings of Boyal Society of Edinburgh . [sess. 
a channel of communication between the primary portions of each 
side. This is the only part of the bladder which is situated below 
the level of the vertebral column. 
The entire bladder, therefore, instead of being composed of 4< two 
lateral halves,” is in reality made up of six parts, — on each side a 
primary portion divided into two by a membrane, and anterior to 
and above this a secondary portion. 
Giinther, in his Introduction to the Study of Fishes , tells us that 
the air bladder and the organ of hearing are connected in a more or 
less simple way in the perch and herring, and by means of a com- 
plicated chain of ossicles in Siluridse, Characinidse, Cyprinidse, and 
Gymnotidse. The details of the Siluroid Amiurus have been worked 
out by Bamsay Wright;* and T. Jeffray Parker has written a On 
the Connection of the Air Bladder and the Auditory Organ in the Red 
Cod (Lotella bacchus)” f Taking these data into consideration, and 
the fact that part of the swimming bladder of Dactylopterus is pro- 
duced into the region of the head, I thought that we might have, 
in this instance, a. similar connection. My most careful dissection 
revealed nothing but the anterior portion of the bladder ending 
blindly in a rigid boundary of bone. Similarly, I might mention 
that I could discover no connection between the bladder and 
alimentary tract, — no pneumatic duct. The amount of gas present 
in the bladder must therefore depend on six retia mirabilia, which, 
horse-shoe shaped, are arranged, three in each primary division of 
the bladder, — two ventrally and one dorsally. 
A. Moreau, in his work Sur la mix des poissons , describes an 
interesting experiment which he made on Trigla hirundo . Observ- 
ing two nerves passing to the air bladder, having their origin below 
the pneumogastric near to the first dorsal pair, he stimulated them 
with electricity and produced the characteristic grunting sounds. 
On studying the bladder, he found in the dividing septum (which 
he calls the diaphragm) both radiating and circular muscular fibres, 
forming a sphincter round the central foramen. On removing the 
posterior end of the bladder and stimulating again, although no sound 
was heard, the sphincter was seen to contract. In the entire bladder, 
* On Anatomy of Amiurus, by Ramsay Wright, M ‘Munich, Mae&lhim, and 
M 4 Kenzie. 
t Trans . N.Z. Instit ., vol. xv. p. 234, 1882. 
