72 THE VITAL FUNCTIONS. 



trasted with that of vegetables. It is a distinctive 

 criterion that applies even to the lowest orders 

 of zoophytes, which, in other respects, are so 

 nearly allied to plants. It extends to all insects, 

 however diminutive ; and even to the minutest 

 of the microscopic animalcules.* 



The mode in which the food is received into 

 the body is, in general, very different in the two 

 organized kingdoms of nature. Plants receive 

 their nourishment by a slow, but nearly constant 

 supply, and have no receptacle for collecting it 

 at its immediate entry; the sap, as we have 

 seen, passing at once into the cellular tissue of 

 the plant, where the process of its gradual elabo- 

 ration is commenced. Animals, on the other 

 hand, are capable of receiving at once large 

 supplies of food, in consequence of having an in- 

 ternal cavity, adapted for the immediate recep- 

 tion of a considerable quantity. A vegetable 

 may be said to belong to the spot from which it 

 imbibes its nourishment; and the surrounding 

 soil, into which its absorbing roots are spread 

 on every side, may almost be considered as a 



part of its system. But an animal has all its 



# 



* In some species of animals belonging to the tribe of Medusas, 

 as the Eudora, Berenice, Oryihia, Favonia, Lymnoria, and 

 Geryonia, no central cavity corresponding to a stomach has been 

 discovered : they appear, therefore, to constitute an exception to 

 the general rule. See Peron, Annales de Museum, xiv, 227 and 

 326. 



