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 medusse, 

 as the Eudora, Berenice, Orythia, 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. 



