DIFFERENCES BETWEEN ANIMALS AND PLANTS. 



not impossible that a limited exception to the universality of 

 the law will be found in the case of animals also. Thus, in 

 some recent investigations into the fauna of the sea at great 

 depths, a singular organism, of an extremely low type, but 

 occupying large areas of the sea-bottom, has been discovered, to 

 which Professor Huxley has given the name of Bathybius. As 

 vegetable life is extremely scanty, or is altogether wanting, 

 in these abysses of the ocean, it has been conjectured that 

 this organism is possibly endowed with the power other- 

 wise exclusively found in plants of elaborating organic com- 

 pounds out of inorganic materials, and in this way supplying 

 food for the higher animals which surround it. The water of 

 the ocean, however, at these enormous depths is richly 

 charged with organic matter in solution, and this conjecture 

 is thereby rendered doubtful. 



Be this as it may, there remain to be noticed two distinc- 

 tions, broadly though not universally applicable, which are 

 due to the nature of the food required respectively by animals 

 and plants. In the first place, the food of all plants consists 

 partly of gaseous matter and partly of matter held in solution. 

 They require, therefore, no special aperture for its admission, 

 and no internal cavity for its reception. The food of almost 

 all animals consists of solid particles, and they are, therefore, 

 usually provided with a mouth and a distinct digestive cavity. 

 Some animals, however, such as the tape-worm and the Gre- 

 garinaB, live entirely by imbibition of organic fluids through 

 the general surface of the body, and many have neither a dis- 

 tinct mouth nor stomach 



Secondly, plants decompose carbonic acid, retaining the 

 carbon and setting free the oxygen, certain fungi forming an 

 exception to this law. The reaction of plants upon the at- 

 mosphere is, therefore, characterised by the production of free 

 oxygen. Animals, on the other hand, absorb oxygen and emit 

 carbonic acid, so that their reaction upon the atmosphere is the 

 reverse of that of plants, and is characterised by the produc- 

 tion of carbonic acid. 



Finally, it is worthy of notice that it is in their lower and 

 not in their higher developments that the two kingdoms of 

 organic nature approach one another. No difficulty is ex- 

 perienced in separating the higher animals from the higher 

 plants, and for these universal laws can be laid down to which 

 there is no exception. It might, not unnaturally, have been 

 thought that the lowest classes of animals would exhibit most 

 affinity to the highest plants, and that thus a gradual passage 

 between the two kingdoms would be established. This is not 

 the case, however. The lower animals are not allied to the 



