INFLUENCE OF THE DEMAND FOR FOOD. 65 



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

 nized kingdoms ot" nature. Plants receive their 

 nourishment by a slow, but nearly constant supply, 

 and have no receptacle for collecting it at its im- 

 mediate entry ; the sap, as we have seen, passing 

 at once into the cellular tissue of the plant, where 

 the process of its gradual elaboration is com- 

 menced. Animals, on the other hand, are capable 

 of receiving at once large supplies of food, in con- 

 sequence of having an internal cavity, adapted for 

 the immediate reception of a considerable quantity. 

 A vegetable may be said to belong to the spot from 

 which it imbibes its nourishment ; and the sur- 

 rounding 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 organs 

 of assimilation within itself; and having receptacles 

 in which it can lay in a store of provisions, it may 

 be said to be nourished from within ; for it is from 

 these interior receptacles that the lacteals, or 

 absorbing vessels, corresponding in their office to 

 the roots of vegetables, imbibe nourishment. Im- 

 portant consequences flow from this plan of struc- 

 ture ; for since animals are thus enabled to subsist 

 for a certain interval without needing any fresh 

 supply, they are independent of local situation, and 

 may enjoy the privilege of moving from place to 

 place. Such a power of locomotion was, indeed, 

 absolutely necessary to beings which have their 

 subsistence to seek. It is this necessity, again, 



cavity corresponding to a stomach has been discovered : they appear, 

 therefore, to constitute exceptions to the general rule, being pro- 

 bably nourished solely by absorption from the surface of the body. 

 See Peron, Annates de Museum, xiv, 227 and 326. 

 VOL. II. F 



