DIFFERENCES BETWEEN ANIMALS AND PLANTS. 21 



lungs of animals, instead of being condensed into one organ, 

 are developed on the stem and branches ; nor is there any 

 organ corresponding to the brain, the heart, the liver, or the 

 stomach. 



62. Moreover, the presence of a proper digestive cavity 

 involves marked differences between the two kingdoms, in 

 respect to alimentation, or the use of food. In plants, the 

 fluids absorbed by the roots are carried to every part of the 

 plant, before they arrive at the leaves ; in animals, on the 

 contrary, the food is at once received into the digestive cavity, 

 where it is elaborated ; and it is only after it has been dis- 

 solved and prepared, that it is introduced into the other 

 parts of the body. The food of animals consists of organized 

 substances, while that of vegetables is derived from inorganic 

 elements ; vegetables produce albumen, sugar, starch, &c., 

 whilst animals consume them. 



63. Plants commence their development from a single 

 point, the seed, and, in like manner, all animals are developed 

 from the egg. But the animal germ is the result of successive 

 transformations of the yolk, while nothing similar takes place 

 in the plant. The subsequent development of individuals is 

 for the most part different in the two kingdoms. No limit is 

 usually placed to the increase of plants ; trees put out new 

 branches and new roots as long as they live. Animals, on 

 the contrary, have a limited size and figure ; and these once 

 attained, the subsequent changes are accomplished without 

 any increase of volume or essential alteration of form ; while 

 the appearance of most vegetables is repeatedly modified, in 

 a notable manner, by the development of new branches. Some 

 of the lowest animals, however, as the polyps, increase in a 

 somewhat analogous manner. 



64. In the effects they produce upon the air, by respira- 

 tion, there is an important difference. Animals consume the 

 oxygen, and give out carbonic acid gas, which is destructive to 

 animal life ; while plants, by respiration, which they, in most 

 instances, perform by means of the leaves, reverse the process, 

 and furnish oxygen, which is essential to the life of animals. If 

 an animal be confined in a small portion of air, or water con- 

 taining air, this soon becomes so vitiated by respiration as to 

 be unfit to sustain life ; but if living plants are enclosed with 

 the animal at the same time, the air is maintained* pure, and 



