122 



MOVEMFAT IN ANIMALS 



preciate the importance of this continuous clearing out 

 of the channels by which air enters the lungs. The most 

 important instance of amceboici movement in the human 

 body is in connection with the wandering of the white 

 blood corpuscles, which help to protect the body against 

 infection by seeking out and engulf- 

 ing disease-producing organisms. 

 The way in which these corpuscles 

 get from place to place among the 

 cells of the body is through 

 amoeboid movement. The chief 

 organs of movement, however, 

 are: 



Muscles. — All the large move- 

 ments of the higher animals are 

 carried on by specialized muscle 

 cells. These will be described be- 

 low. Here we wish only to say that 

 they represent a marked example 

 of the division of labor which was 

 discussed in Chapter III. Muscle 

 cells are composed of living proto- 

 plasm which has the contractile 

 property highly developed and the 

 other properties correspondingly re- 

 duced. The functional metabolism 

 of muscle cells consists in the per- 

 forming of these contractions, in 

 other words, in the conversion of chemical energy 

 into the energy of motion. 



The Biological Importance of Motion. — Before 

 going on to a further description of muscular action, let 

 us take a moment to inquire into the utility to animals 

 of the power to move. 



(1) Primarily Motion in Animals is a Means of Secur- 

 ing Food. — All animals require for their food complex 

 substances which result either directly or indirectly from 



Fi(5. 29. — DijiRram of 

 the Protozoan, Vorti- 

 cella, shown in the 

 normal extendcHi posi- 

 tion, and also partially 

 contrartod. The pro- 

 toplasmic strand by 

 which contraction is prf>- 

 duced is shown extend- 

 ing down the stem. 



