26 DISTINCTIVE CHARACTERS OF 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 Lntozoa (§ 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 2hizopoday 
(§ 129), in which, notwithstanding the absence of any regulan 
stomach, the food is.received into the very substance of the) 
jelly-like particle of which the body consists; a mouth and 
