DIGESTIVE ORGANS OF FISHES. 



195 



tongue folded back ; o, the oesophagus ; and s, the 

 stomach, from which the tortuous intestinal tube 

 is seen to be continued. All the convolutions of 

 this tube, as well as the stomach itself, are enclosed, 

 or rather imbedded in the substance of the liver, 

 which is the largest organ of the body. 



The PleurohranchiLs Peronii (Cuv.) is remark- 

 able for the number and complication 

 of its organs of digestion. They are 

 seen laid open in Fig. 330 ; where c is 

 the crop ; g, the gizzard ; p, a plicated 

 stomach, resembling the third stomach 

 of ruminant quadrupeds ; and d, a 

 fourth cavity, being that in which di- 

 gestion is completed. A canal of com- 

 munication is seen at t, leading from 

 the crop to this last cavity ; b is the 

 point where the biliary duct enters. 

 The digestive apparatus of the Aplysia 

 is still more complicated ; it comprises a gizzard, 

 beset with numerous pyramidal cartilages placed 

 in rows on its internal surface, their apices meeting 

 in the centre of the cavity : they evidently serve 

 the mechanical purpose of bruising and grinding 

 the food, and of allowing none to pass luiless finely 

 comminuted. 



In the Cephalopoda the structure of these organs 

 is very complicated ; for they are provided with a 

 crop, a muscular gizzard, and a caecum, which has 

 a spiral form. In these animals we also discover 

 the rudiment of another auxiliary organ, namely, 

 the Pancreas, which secretes a fluid contributing 

 to the assimilation of the food. This organ becomes 

 more and more developed as we ascend in the scale 



