DIFFERENCES BETWEEN ANIMALS AND PLANTS 219 



cilia, and occur only in small numbers on any cell, one or two 

 being the usual number. Higher animals do not have true 

 flagella, except in their sperms; see page 250. (3) Muscular 

 Movements. In all animals above the unicellular forms cer- 

 tain cells, or parts of cells, become specially modified for con- 

 traction, thus becoming muscles. These develop into a system 

 which produces the many types of locomotion possessed by 

 animals. 



While plants as a rule are stationary, a few of them possess 

 independent motion. Spores of many plants possess flagella 

 or cilia; some of the lowest show amoeboid motion, and some 

 have methods of motion not yet understood, like Diatoms and 

 Osdllaria; Fig. 68. Among higher plants movements of different 

 parts of the leaves, stamens, etc., are not uncommon. No 

 muscles are developed, however, in plants, the motions being 

 due to slow changes in the protoplasm, which are not well 

 understood. An independent locomotion is unknown among 

 any plants except those of the lowest orders. 



C. Sensitiveness. In order to distinguish their food, ani- 

 mals have developed sensitiveness and sensations. Plants not 

 needing to distinguish food so accurately have not developed 

 much sensitiveness. 



D. Structure. As a rule animals have their bodies con- 

 densed into a small compass, and are provided with an opening 

 for taking in food, the mouth, which is connected with a 

 digestive system. Typical plants, since they feed upon gases 

 and water, which are distributed everywhere, have their bodies 

 widely expanded into branches, leaves, and root hairs, in order 

 to come in contact with a large amount of air and soil. They 

 never have any mouths, since they do not take solid food, 

 and consequently have no digestive system. 



The Income and Outgo of Animals and Plants. An animal 

 has an income as follows : 



Proteids, obtained from animal or vegetable food, but all 

 originally derived from green plants. 



