24 ELEMENTS OF BIOLOGY. 



by the passage of the food into living tissue. Plants, there- 

 fore, are the great manufacturers in nature, animals are the 

 great consumers. 



Just, however, as this law does not invariably hold good 

 for plants, certain fungi being in this respect animals, so it 

 is 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 dis- 

 covered, 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 — otherwise exclusively found in plants — of 

 elaborating organic compounds 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 aper- 

 ture for its admission, and no internal cavity for its recep- 

 tion. 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-w^orm and the Gregarinae, live 

 entirely by the imbibition of organic fluids through the 

 general surface of the body, and many have neither a 

 distinct mouth nor stomach. 



Secondly, plants decompose carbonic acid, retaining the 

 carbon and setting free the oxygen, certain fungi forming 







