240 MICROSCOPIC FOEMS OF VEGETABLE LIFE. 



being again claimed as members of the Animal Kingdom, — and 

 lastly, on the discovery of a fallacy in these arguments, being once 

 more turned over to the Botanist, with whom, for the most part, 

 they now remain. For the attention which has been given of late 

 years to the study of the humblest forms of Vegetation, has led 

 to the knowledge, among what must be undoubtedly regarded as 

 Plants, of so many phenomena which would formerly have been 

 considered unquestionable marks of Animality, that the discovery 

 of the like phenomena among the doubtful beings in question, so 

 far from being any evidence of their Animality, really affords a 

 probability of the opposite kind. 



ISO. In the present state of Science it would be very difficult, 

 and is perhaps impossible, to lay down any definite line of demar- 

 cation between the two Kingdoms ; since there is no single character 

 by which the Animal or Vegetable nature of any Organism can 

 be tested. Probably the one which is most generally applicable 

 among those lowest Organisms that most closely approximate to one 

 another, is — not, as formerly supposed, the presence or absence of 

 Spontaneous Motion, — but the dependence of the being for nutri- 

 ment upon Organic Compounds already formed, which it takes 

 (in some way or other) into the interior of its body ; or, on the other 

 hand, its possession of the power of producing the Organic Com- 

 pounds which it applies to the increase of its fabric, at the expense 

 of certain Inorganic Elements (Oxygen, Hydrogen,. Carbon, and 

 Nitrogen) which it obtains ' by decomposing the Water, Carbonic 

 Acid, and Ammonia with which it is in external relation. The 

 former is the characteristic of the Animal Kingdom as a whole ; 

 the latter is the attribute of the Vegetable ; and although certain 

 apparently exceptional cases may exist, yet these do not seem to 

 occur among the group in which such a means of distinction is most 

 useful to us. For we shall find that those Protozoa, or simplest 

 Animals, which seem to be composed of nothing else than a mass 

 of living jelly (Chaps, ix. x.), are supported as exclusively either 

 upon other Protozoa or upon Protopltytes (which are humble Plants 

 of equal simplicity), as are u the highest Animals upon the flesh of 

 other Animals or upon the products of the Vegetable Kingdom : 

 whilst these Protophytes, in common with the highest Plants, draw 

 their nourishment from the Atmosphere or the Water in which they 

 live, and are distinguished by their power of liberating Oxygen 

 through the decomposition of Carbonic Acid under the influence of 

 San-light. And we shall moreover find that even such Protozoa as 

 have neither stomach nor mouth, receive their alimentary matter 

 direct into the very substance of their bodies, in which it under- 

 goes a kind of digestion ; whilst the Protophyta absorb through 

 their external surface only, and take in no solid particles of any 

 description. With regard to Motion, which was formerly con- 

 sidered the distinctive attribute of Animality, we now know not 

 merely that many Protophytes (perhaps all at some period or other 



