CHAPTER FIFTH. 



OF MOTION. 





 SECTION I. 



APPARATUS OF MOTION. 



148. THE power of voluntary motion is the second grand 

 characteristic of animals, (57.) Though they may not all 

 have the means of transporting themselves from place to 

 place, there is no one which has not the power of executing 

 some motions. The oyster, although fixed to the ground, 

 opens and closes its shell at pleasure ; and the little coral 

 animal protrudes itself from its cell, and retires again at 

 its will. 



149. The movements of animals are effected by means of 

 muscles, which are organs designed expressly for this pur- 

 pose, and which make up that portion of the body which 

 is commonly called flesh. They are composed of threads, 

 which are readily seen in boiled meat. These threads 

 are again composed of still more delicate fibres, called mus- 

 cular flbres, (45,) which have the property of elongating 

 and contracting. 



150. The motions of animals and plants depend, therefore, 

 upon causes essentially different. The expansion and cloe'ng 

 of the leaves and blossoms of plants, which are their most 



