DISTINCTIVE CHARACTERS OF ANIMALS. 25 
great as that which exists among the lowest animals ; so that 
no positive line can be drawn between the two kingdoms on 
the basis of this distinction alone. There is another very 
important physiological difference, however, between the two 
kingdoms, which seems to afford an adequate means of 
settling the true place of those tribes whose position would 
otherwise be doubtful. This lies in the nature of their food, 
and the source from which it is obtained. For although it-is 
now known that the primary tissues of plants are originally 
formed of the same albuminous material as are those of 
animals (the cellulose layers which constitute the great 
bulk of the vegetable fabric being a subsequent deposit), yet 
this material is generated in the Plant by the combination of 
the elements which it obtains from the carbonic acid, water, 
and ammonia of the soil or-of the atmosphere; whilst the 
Animal is destitute of all power of thus forming it for itself, 
and is hence entirely dependent upon the plant for its sup- 
van of nutriment. Thus, whilst the very humblest forms of 
egetation, in common with the highest, are found to have 
the power of decomposing carbonic acid under the influence 
of sunlight, setting free its oxygen and retaining its car- 
‘bon, the humblest forms of Animal life, in common with 
‘the highest, derive their nutriment either directly from 
plants, or from the bodies of other animals which have sub- 
‘sisted on vegetable food, whilst they produce a converse 
change in the atmosphere by their respiration, absorbing 
from it oxygen, and giving forth to it carbonic acid. This 
ces taken in as food, affords a strong probability of their 
table character; these colours being produced in the 
