22 DIFFERENCES BETWEEN ANIMALS AND PLANTS. 



no difficulty is experienced. The practical effect of this com- 

 pensation, in the economy of nature, is obviously most im- 

 portant ; vegetation restoring to the atmosphere what is con- 

 sumed by animal respiration, combustion, &c., and vice versa. 



65. But there are two properties which, more than all 

 others, distinguish the animal from the plant, namely, the 

 power of moving itself or its parts at will, and the power of 

 perceiving objects and the influences produced by them ; in 

 other words, voluntary motion and sensation. 



66. All animals are susceptible of pleasure and pain. 

 Plants have also a certain sensibility. They wither and fade 

 under a burning sun, or when deprived of moisture ; and they 

 die when subjected to too great a degree of cold, or to the 

 action of poisons. But they have no consciousness, and there- 

 fore suffer no pain ; while animals under similar circum- 

 stances endure it. Hence they have been called animate beings, 

 in opposition to plants, which are inanimate beings. 



[ 67. If we take a general view of the animal and vegeta- 

 ble kingdoms, we find that each kingdom may be grouped 

 into three divisions. 



IN THE ANIMAL. IN THE VEGETABLE. 



1. Zoophyta. 1. Acotyledons. 



2. Mollusca and Articulata. 2. Monocotyledons. 



3. Vertebrata. 3. Dicotyledons. 



[ 68. The first great division of the animal series compre- 

 hends the zoophytes ; their bodies have a circular or radiated 

 form like some of the lowest vegetables, and are composed of a 

 simple organic tissue, which is soft, pulpy, more or less trans- 

 parent, and possessed of irritability and contractibility, although 

 muscular fibres have not been observed in many groups of 

 this division. They manifest a high degree of sensibility, 

 although distinct nerves and ganglia have been only discovered 

 in the acalephae and echinodermata. In these classes the gan- 

 glia form so many centres of life, and each segment of the 

 body has its own special ganglion. Through this simple con- 

 dition of the nervous system many zoophytes possess the 

 power of reproduction by scission or slips, and by buds or 

 gemmules, after the manner of plants. The most inferior 

 forms have no distinct organ except a digestive cavity, which 



