10 ZOOLOGY. 



2. Characteristic Differences between Plants and Ani- 

 mals. Both, plants and animals are organic bodies. They 

 both possess life, and are able to propagate their kind. 

 Although it v is generally easy to distinguish between 

 plants and animals, yet there is a border land in which 

 it is difficult to determine where the one kingdom ends 

 and the other begins. The following are the most char- 

 acteristic differences of the two kingdoms ; but, as will 

 be seen, the distinctions can scarcely be looked upon as 

 universal. 



3. Chemical Composition. Most of the characteristic 

 substances found in plants, such as starch, sugar, &c., are 

 composed of three elements carbon, oxygen, and hydro- 

 gen. On the other hand, albumen and fibrine, so abun- 

 dantly met with in animal tissues, are composed of four 

 elements carbon, oxygen, hydrogen, and nitrogen. This 

 distinction, however, is not universal, as compounds of 

 the three elements are met with in animals, while nitro- 

 gen is present in several vegetable products. 



4. Peeling or Sensibility was selected by Linnaeus as 

 the leading characteristic of the animal kingdom. In 

 such animals as possess a nervous system, the distinction 

 is worthy of the position assigned to it by the great 

 naturalist. But when it is remembered that two primary 

 groups of animals, the Protozoa and the Ccelenterata, are 

 utterly devoid of a nervous system, the characteristic 

 fails to be universally applicable. 



5. Locomotion. This characteristic, which is so marked 

 in the higher groups, also fails when we reach the more 

 lowly organisms. Many of these, such as the sponges, 

 corals, and corallines, are as much confined to a particular 

 spot as plants are. On the other hand, many minute 

 aquatic plants, such as the Diatomacese, are able to move 

 about with great rapidity. 



6. Organs of Digestion. The possession of a re- 

 ceptacle, in which to deposit and digest their food, is a 

 feature broadly distinctive of the animal kingdom. Many 

 of the Protozoa, however, are destitute of any permanent 



