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 
