STRUCTURE OF FISHES. 



13 



whole duration of their lives ; the only teeth \vliich are retained permanently being those in the 

 rostrum of Pristis, the dental masses of Chimaera, and a few others. 



The lips of fishes are not much developed ; in Sharks and Rays they are supported by cartilages. 

 In the Cod there are fringed filaments between the lips and the teeth, and in several fishes there are 

 tentacles attached to the lips, which assist in selecting food. There are no proper salivary glands in 

 fishes, and the tonsils are entirely absent. The alimentary canal is usually short and large ; in the genus 

 Lepidosiren it is almost straight. The front part, termed the oesophagus, is a funnel-shaped canal 

 coated with a strong muscular substance, so that it grasps the food and passes it downward into the 

 stomach. In many fishes the pneumatic duct from the air-bladder opens into the oesophagus, and in 

 the Ganoid fishes the entrance to this canal is controlled by muscles. The stomach is usually a large 

 simple cavity, with a capacious inlet and a small outlet. Sir R. Owen defines two kinds of stomach 

 in fishes : first, the enlarged bent tube seen in the Cod, Salmon, Tench, Sturgeon, and most Sharks ; 

 and secondly, the form seen in the Perch, Gurnards, Smelts, Pike, Herring, Sprat, and Eel, in which 

 the stomach forms a sort of pouch. It is 

 rare for the stomach to be globular, but this 

 condition is seen in the genus Mormyrus. 

 The stomach takes on some of the characters 

 of a gizzard, and in several fishes this organ 

 is more or less divided into two or three 

 chambers. The juice secreted by this organ 

 has a rapid action on food, and it sometimes 

 happens that the part of an animal contained 

 in the stomach is dissolved, while the part 

 which remained in the oesophagus is entire. 

 Fishes disgorge the indigestible part of their 

 food, and when caught frequently eject the 

 animals they have swallowed. The intestine 

 beyond the stomach is often short and simple. 

 Round its commencement in most osseous 

 fishes there ai % e a number of slender pouches, 

 which represent the sweetbread or pancreas of 

 higher animals, but in the Lamprey and Hag 

 there is no trace of a pancreas, and in a few 

 fishes there is only a single filament to repre- 

 sent it; in the Turbo t there are but two, and 

 in the Perch three ; in the Sprat there are 

 as many as nine, but in the Salmon they are 

 more numerous, and extend along the whole 

 length of the first part of the small intestine, 

 which is technically called the duodenum. 

 In the Whiting this organ forms a fringe 

 like a collar around the beginning of the 

 intestine, and in the Sturgeon the pancreas 

 becomes more compact, and pours its secre- 

 tion into the intestine by a single wide duct. 

 Sometimes the pancreas is heavier than the 

 liver. 



The liver in fishes is generally large, and 

 consists of two lobes ; it is soft, and usually 

 yellowish-brown, but varies in colour in different fishes, being sometimes white, yellow, orange, green, 

 bright red, and occasionally nearly black. It is an organ in which much of the oil of the body becomes 

 accumulated, though fat fishes have very little oil in the liver. The liver varies in form with the 

 shape of the body, being broad in the Rays and long in the Eels. It is greatly divided in the Tunny. 



INTERNAL ANATOMY OF THE CARP. 



6r, Bronchia?, or Gill.*: c, Heart: /, T.tver; vn. vn', Swinnuinsr TMadder; 

 ci, Intestinal Canal; o, Ovaries; u, Urethra; o, Anus ; o', Oviduct. 



