2 ANIMAL FORMS 



greater number of more highly developed species the line 

 of separation is clearly marked. It is very easy, for example, 

 to distinguish the oak-tree or the rose from a horse or a 

 butterfly, and, as we shall see, the differences are not based 

 merely on outward appearance. 



In the oak-tree, for example, the roots reaching down 

 into the earth, with the branches and leaves spreading out 

 into the air and sunlight, are admirably fitted for taking up 

 the food, which consists of very simple materials, less com- 

 plex than those forming the diet of an animal. This 

 permits a continuous existence in one place, and accord- 

 ingly we note the entire absence of locomotion and the or- 

 gans controlling it, which form so conspicuous a part of the 

 body of an animal. Also in the production of flowers and 

 seeds, and in the growth of the seed into the tree, we detect 

 many characteristics peculiar to plants. 



3. Characteristics of an animal On the other hand, the 

 squirrel, for example, or any other animal, is unable to sub- 

 sist on water, air, and elements from the soil. These crea- 

 tures demand the highly diversified materials found in the 

 bodies of plants and of animals. Such being the case, they 

 do not remain anchored to one spot (except in a relatively 

 few cases), but are compelled to lead an active existence. 

 The power of voluntary movement, or movement in response 

 to internal impulse, is thus the first and one of the most 

 striking peculiarities of animals. 



In the second place, the food of plants enters the body 

 in a soluble condition and is readily transferred to the or- 

 gans requiring it. While in the animals, the nutritive ma- 

 terials pass into the body in an insoluble state and de- 

 mand a varied preliminary treatment, usually within a 

 special digestive tube, before they are fit to be absorbed. 

 In the squirrel, by way of illustration, the food is first 

 ground to a pulp by the action of the teeth, and, moistened 

 with saliva, is swallowed and passed into the stomach, 

 where it is subjected to the solvent action of the gastric 



