DIFFERENCES BETWEEN ANIMALS AND PLANTS. I/ 



To this general statement, however, an exception must be 

 made in favour of certain Fungi, which require ready-made 

 organic matter for their nourishment There are also certain 

 plants (such as the Sun-dew and the Venus' Fly-trap) which 

 live to some extent upon animal food. 



On the other hand, no known animal possesses the power 

 of converting inorganic compounds into organic matter, but 

 all, mediately or immediately, are dependent in this respect 

 upon plants. All animals, as far as is certainly known, require 

 ready-made proteinaceous matter for the maintenance of exist- 

 ence, and this they can only obtain in the first instance from 

 plants. Animals, in fact, differ from plants in requiring as food 

 complex organic bodies which they ultimately reduce to very 

 much simpler inorganic bodies. The nutrition of animals is 

 a process of oxidation or burning, and consists essentially in 

 the conversion of the energy of the food into vital work ; this 

 conversion being effected by the passage of the food into living 

 tissue. Plants, therefore, are the great manufacturers in nature, 

 animals are the great consumers. 



There remain to be noticed two distinctions, broadly though not uni- 

 versally applicable, which are due to the nature of the food required re- 

 spectively 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 in- 

 ternal 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- 

 worms 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 set- 

 ting free the oxygen, certain fungi forming an exception to this law. The 

 reaction of plants upon the atmosphere 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 production of car- 

 bonic 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 experienced in separating the higher animals 

 from the higher plants, arid, 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 higher plants, but to the lower ; and it is in the very 

 lowest members of the vegetable kingdom, or in the embryonic and im- 

 mature forms of plants little higher in the scale, that we find such a de- 

 cided animal gift as the power of independent locomotion. It is also in 

 the less highly organised and less specialised forms of plants that we find 



B 



