i8o Elementary Zoology. 



animals rarely do ; that the nourishment of plants is never 

 taken in as solid particles, while that of animals nearly always 

 is, to some extent. 



2. A point of unlikeness between animals and plants that 

 is often emphasized is the power of locomotion possessed by 

 the one group and deficient in the other. Broadly speaking, 

 it is true that animals move from place to place, and that plants 

 do not. With the higher plants it is' rigidly true. The cause 

 for this is to be found in the histological structure of plants ; 

 each cell being enveloped in a stiff cell-wall is, of itself, 

 sufificient to prevent locomotion. That this is so is proved 

 by the fact that simple naked plants, such as simple algse, 

 " Flowers of Tan," } etc., do move, and rapidly, from place 

 to place. But, though there is but little locomotion, there 

 is plenty of movement among plants. We need not refer to 

 the bursting of seed-vessels, which are due to purely physical 

 causes, such as the swelling and consequent rupture of certain 

 parts. But genuine movements of protoplasm, often affecting 

 a considerable part of the plant, take place. It is enough to 

 remind the student of the sensitive plant of the folding and 

 unfolding of flowers at night and morning, etc. 



These are the principal physiological differences between 

 animals and plants. We shall now discuss their morphological 

 unlikeness. 



I. The shapes of animals and plants markedly differ. 

 Apart from the unicellular forms, the animal has usually a 

 symmetrical and very solid body. The plant is, as a rule, not 

 symmetrical ; the body is much made of flat expansions. This 

 difference, though morphological, really depends upon the 

 physiological considerations already dealt with. The plant 

 being stationary, and feeding upon gases and fluids, has to 

 have as large a surface as possible for their absorption, and 

 to ramify as much as possible for the purpose of collecting the 

 food gases and fluids. 



Animals, on the other hand, are, as a rule, locomotive, and 

 hence their prevailing bilateral symmetry; when they are 



' This organism is, however, considered an animal by perhaps most 

 naturalists. 



