160 



THE VITAL FUNCTIONS. 



/ 



organ, namclvj the Panaceas, which secretes a fluid contri- 

 buting to tlie assimihitfon of the food. This organ becomes 

 more and more developed as we ascend in the scale of ani- 

 mals, assuming a glandular character, and secreting a watery 

 fluid, which resembles the saliva, both in its sensible and 

 chemical properties. It has been conjectured that many of 

 the vessels, which are attached to the upper portion of the 

 alimentary canal of insects, and have been termed hepatic, 

 may, in fact, prepare a fluid having more of the qualities of 

 the pancreatic than of the biliary secretion. 



The alimentary canal of fishes is in general characterized 

 by being short; and the continuity of the stomach with the 

 intestines is often such as to. oflcr no well marked line of 

 distinction between them. The ca3ca are generally large and 

 numerous; and a number of tubular organs, connected more 

 especially with the pyloric appendices, arc frequently 

 met with, resembling a cluster of worms, and having some 

 analogy, in situation at least, to the hepatic or pancreatic 

 vessels of insects. Their appearance in the Sabyion is re- 

 presented at p, in Fig. 331. The pancreas 

 itself is only met with, in this class of ani- 

 mals, in the order of cartilaginous fishes, and 

 ire especially in the Ray and the Shark 

 tribes. A distinct gall-bladder, or reservoir, 

 is also met with in some kinds of fish, but is 

 by no means general in that class. 



In the class both of Fishes and of Reptiles, 

 which are cold-blooded animals, the processes of digestion 

 are conducted more slowly than in the more energetic sys- 

 tems of Birds and of Mammalia; and the comparative 

 length of the canal is, on the whole, greater in the former 

 than in the latter: but the chief diflcrenccs in this respect 

 depend on the kind of food which is consumed, the canal 

 being always shortest in those tribes that are most carnivo- 

 rous.^ As the Frog, in the different stages of its growth. 



• See Home, Lectuies, &c. I. 401. 



