14 ORGANS OF NUTRITION OF FISHES. 



which amongst the Rays, &c. form the jaws, are here united into 

 rings, and support a fleshy disc, the surface 

 of which is furnished with teeth, whilst 

 its centre is occupied by the mouth. The 

 tongue also is supplied with teeth, and 

 moves forwards and backwards like a 

 W m? I Pi ston so tnat tne animal can make use 

 of this apparatus, either to fix itself upon 

 FIG. 257.-MOUTH OF THE ailot her body, or to pump up the fluids on 



LAMPREY. ' ' 



which it is supported. 



534. The mouth is not surrounded by any salivary gland. 

 The oesophagus is short ; the stomach and the intestines vary in 

 size and form. The liver is generally large, and of a soft tissue ; 

 the pancreas is nearly always replaced by peculiar ccecal appen- 

 dages placed around the pylorus ; the position of the anus varies 

 much ; sometimes it is found under the throat, at other times 

 under the tail. The kidneys are extremely large, and extend 

 themselves on both sides of the vertebral column, through the 

 whole length of the abdomen. Their excretory passages end in 

 a kind of bladder, whose external opening is placed immediately 

 behind the anus and the orifice of the reproductive organs. The 



-digestive process appears to be performed very rapidly ; and the 

 chyle is absorbed by numerous lymphatic vessels, which empty 

 themselves by several trunks into the venous system near the 

 heart. 



535. The blood of Fishes, as already mentioned, is red ; and 

 the globules have an elliptical form, and are of considerable 

 dimensions. The heart is placed under the throat, in a cavity 

 divided from the abdomen by a kind of diaphragm, and protected 

 by the pharyngeal bones above, by the branchial arches on the 

 sides, and in general by the humeral girdle behind. It is com- 

 posed of one auricle, which receives the venous blood collected 

 into a large sinus situated in its neighbourhood ; and of a ven- 

 tricle placed beneath it, and giving rise at its anterior extremity 

 to a pulmonary artery, which is swollen out at its origin into a 

 contractile bulb. This vessel soon divides into lateral branches, 

 which are distributed to the gills ; and the blood, after having 



