ALIMENTARY CANAL, ETC., OF AMIURUS CATUS. 417 
jelly-like mass. These fibres are arranged in every direction, but for 
the most part longitudinally, then transversely. The longitudinal 
fibres are generally outside. In acetic acid the jelly mass shows 
stringy portions arranged parallel, not constantly, however. The 
second set, or elastic fibres, are very numerous, and show an exten- 
sive branching and inter-communication sometimes surrounding, 
sometimes penetrating, the bundles of gelatinous matter. 
The inner coat, the membranous wall of the bladder cavities, con- 
sists of a layer of flat hexagonal cells, and outside this a fibrous layer. 
The flattened epithelium is disposed alike over the inner surface and 
does not differ in development over the capillaries, as has been de- 
scribed to be the case in other fishes. The contents of each cell are 
clear and the nucleus is round and conspicuous. The mucous layer 
beneath consists of connective tissue fibres not very closely arranged. 
No elastic fibres were found. No muscle fibres could be made out 
either plain or striated. 
The blood supply of the air-bladder is obtained from the arteria 
celiaca, the vessel entering the organ at the origin of the duct, and, 
after giving several branches to the outer coat, it enters the inner 
membranous coat, and is there ultimately distributed. It divides 
into two main branches and several smaller ones ; the main branches 
pass one to each side on the walls of the posterior chambers, while 
the smaller ones traverse the walls of the anterior chamber. Each 
branch is accompanied by a vein arranged both in such a manner 
that the two are in parallel course and side by side. Both branch 
simultaneously, and. the different branches are again connected after 
some distance by capillaries. It also often happens that the area 
supplied by one branch also possesses some of the capillaries and 
finer twigs of a second branch. Usually each fine arterial branch has 
a region set apart, and there it ultimately divides into fine anastom- 
osing capillaries which are drained by various capillaries also origin- 
ating in the same way. 
The larger venous branches are very often varicose, appearing often 
like sinuses. 
There is no blood-gland in the air-bladder of Amiurus in the sense 
in which that word is used. 
The blood of the air-bladder is collected in the mesenteric veins 
and carried onward to the heart. 
