DISTINCTION BETWEEN PLANTS AND ANIMALS. 247 



evidently plant-like mode of growth, being transferred back to 

 the Botanical side, then, owing to the supposed detection of 

 some new feature in their structure or physiology, being again 

 claimed as members of the Animal Kingdom, and lastly, on 

 the discovery of a fallacy in these arguments, being once more 

 laid hold of by 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 of so many phenomena, among what must be 

 undoubtedly regarded as Plants, 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. 



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

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

 marcation between the two kingdoms ; since there is no single 

 character by which the Animal or Vegetable nature of any or- 

 ganism can be tested. Probably the one which is most generally 

 applicable, among those lowest organisms which 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 nutriment upon organic compounds already 

 formed, which it takes (in some way or other) into the interior 

 of its body, or its possession of the power of obtaining its own 

 alimentary matter by absorption, from the inorganic elements on 

 its exterior. 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 w r hich such a 

 means of distinction is most useful to us. For we shall find 

 that those Protozoa, or simplest Animals, which seem to be com- 

 posed of nothing else than a mass of living jelly (Chaps. IX, X), 

 are supported as exclusively, either upon other Protozoa, or upon 

 Protophyta, which are humble Plants of equal simplicity, as the 

 highest Animals are upon the flesh of other animals, or upon 

 the products of the Vegetable Kingdom ; whilst these Pro- 

 tophy tes, in common with the highest Plants, draw their nourish- 

 ment from water, carbonic acid, and ammonia, and are distin- 

 guished by their power of liberating oxygen, through the 

 decomposition of carbonic acid, under the influence of sunlight. 

 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 



