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 

 fibi'es 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 drteria 

 aeliaca, 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. 



