CHAPTER IX 



MOTION AND LOCOMOTION. THE SKELETON 



EVERY organism is capable of exhibiting motion in 

 some part, even though such movement may be 

 visible only with the aid of a microscope. Most 

 animals, are capable of locomotion, or movement 

 from place to place, while but few plants have 

 that power. The power of movement possessed 

 by the animal and the fixed condition of the 

 plant forms a popular distinction between the 

 two branches of the organic world, but although 

 for the most part ignored as a characteristic 

 difference by science, it is still worthy of close 

 attention, since it is bound up with other 

 differences which are fundamental. 



We have said that most animals are capable of 

 locomotion, and that this is necessary to their 

 existence, since, without that power, it would be im- 

 possible for them to obtain organic food, which is 

 only local in distribution. Fixed animals, such as 

 zoophytes, sea- anemones, barnacles, &c., live in a 

 medium, the sea, wherein organic food is distributed 

 more uniformly and where currents of water bring 

 the organic food to them, just as atmospheric currents 

 bring the necessary carbon-dioxide to the plant. 

 On the other hand, the vast majority of plants are 

 fixed organisms, but the raw materials which they 

 require for the purpose of constructing organic 

 compounds are to be found everywhere ; there is 

 no need to move about in search of them. Loco- 



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