26 DISTINCTIVE CHARACTERS OP ANIMALS. 



course of that series of chemical changes, by which, under the 

 influence of light, the living plant can unite, inorganic elements 

 into organic compounds. 



8. Not only do Animals differ from Plants in the nature 

 and sources of their aliment, but also in the mode in which, 

 it is taken into their bodies ; and this difference is related 

 alike to the character of the food of animals, and to the general 

 conditions of animal existence. For the Plant extends its 

 roots through the soil in search of liquid, and spreads out its 

 leaves to the air for the purpose of imbibing some of its 

 gaseous ingredients. But the Animal could not so exist, and 

 be at the same time endowed with the power of moving from 

 place to place ; nor could it appropriate solid nutriment, if it 

 were not provided with some peculiar means of receiving and 

 preparing this. For these purposes, animals (with few 

 exceptions) are provided with an internal cavity or stomach 

 into which the food is received from time to time, in which 

 it can be carried about in the general movements of the body, 

 and within which it can be prepared for being received by 

 absorption into the current of nutrient liquid which circu- 

 lates through the body. This stomach is nothing else than a 

 bag formed by the prolongation of the external covering of 

 the body into its interior ( 36); its cavity receives the food 

 introduced into it by the mouth ; its walls pour out or secrete 

 a fluid which acts upon the food in such a manner as to dis- 

 solve it ; and through its walls are absorbed those portions 

 of the food which are fit to be employed as nutriment, while 

 the remainder is cast forth from the cavity, either by the 

 aperture which first admitted it, or by a distinct orifice. The 

 exceptional cases, in which no stomach exists, chiefly occur 

 in one particular tribe of animals, the Entozoa ( 105), which 

 live either in the intestinal canal or in the substance of the 

 tissues of other animals, and which are supported by the 

 nutrient juices of these ; such an organ obviously not being 

 required by creatures which have no power of locomotion, 

 and which can imbibe liquids already prepared for their use, 

 through the whole of the soft surface of their bodies. But 

 there is a large tribe of very simple animals, the Rhizopoda 

 ( 129), in which, notwithstanding the absence of any regular 

 stomach, the food is.. received into the very substance of the 

 jelly-like particle of which the body consists ; a mouth and 



