INTERNAL ANATOMY. 



11 



vertebrates, but we shall have no occasion to discuss these points in European 

 fresh-water fishes. 



AlR-BlADDER. 



There is no air-bladder in the Lampreys, and the organ cannot be con- 

 sidered to show a respiratory function in any of the fresh-water fishes of 

 Europe. It is commonly placed below the vertebral column in the abdo- 

 minal cavity, and in most cases' 

 tapers in front and behind. 

 In an early stage of existence 

 the air-bladder communicates 

 with the intestine by a duct, 

 which is obliterated in many 

 genera as the fish attains maturity. In the Carp tribe the air-bladder is con- 

 structed so as to form anterior and posterior divisions (Fig. 7), and in the Loach 

 tribe it consists of two parallel portions, which are contained in bony capsules 

 at the sides of the anterior vertebrae. In the Sturgeon it is thick, and con- 

 sists of several layers. 



DIGESTIVE ORGANS (Figs. 8, 9). 



Sometimes the intestine is simple, as in the Lamprey, in which it is 

 difficult to separate the parts which are usually named oesophagus, stomach, 



Fig. 7. AIll-HLADDEl 



Fig. 8. INTERVAL AXATOMY OF CARP. 



ftr, branchiae or gills ; c, heart; /, liver; vn, vn', air-bladder; ci, intestinal canal; n, urethra. 



and intestine. In the Sturgeons the intestine is complicated, and receives 

 the secretion from the liver and the pancreas, and terminates in a spiral 

 valve, like that seen in Sharks. The form of the stomach varies, sometimes 

 making a blind snc, and sometimes being an expanded part of the intestine, 

 situate at an angular bend in its course. Behind the stomach, the intestine 

 frequently carries a fringe of appendages, known as pyloric appendages, which 

 are greatly developed in the Salmon tribe, and vary in number in the different 



