WITH VEGETABLES. 5 



living upon organic matter would seem to be less decisive 

 of an animal nature, for some fungi appear to derive 

 support almost entirely from this source. 



II. There is, commonly, a marked difference in general 

 chemical composition between vegetables and animals, 

 even in their lowest forms ; for while the former consist 

 mainly of a substance containing carbon, hydrogen, and 

 oxygen only, arranged so as to form a compound closely 

 allied to starch, and called cellulose, the latter are com- 

 monly composed in great part of the three elements 

 just named, together with a fourth, nitrogen ; the proxi- 

 mate principles formed from these being identical, or 

 nearly so, with albumen. It must not be supposed, how- 

 ever, that either of these typical compounds alone, with 

 its allies, is confined to one kingdom of nature. Nitro- 

 genous or albuminous compounds are freely produced 

 by vegetable structures, although they form an infinitely 

 smaller proportion of the whole organism than cellulose or 

 starch. And while the presence of the latter in animals 

 is much more rare than is that of the former in vegetables, 

 there are many animals in which traces of it may be dis- 

 covered, and some, the Ascidians, in which it is found in 

 considerable quantity. 



III. Inherent power of movement is a quality which we 

 so commonly consider an essential indication of animal 

 nature, that it is difficult at first to conceive it existing in 

 any other. The capability of simple motion is now known, 

 however, to exist in so many vegetable forms, that it can 

 no longer be held as an essential distinction between them 

 and animals, and ceases to be a mark by which the one 

 can be distinguished from the other. Thus the zoospores 

 of many of the Cryptogamia exhibit movements of a like 

 kind to those seen in animalcules ; and even among the 

 higher orders of plants, many exhibit such motion, either 

 at regular times, or on the application of external irrita- 

 tion, as might lead one, were this fact taken by itself, to 



