36 ANIMAL LIFE 



a small fragment, cause this to move. Mahomet, as 

 it were, comes to the mountain. 



But the gill of shellfish is not the only place where 

 ilia are found inside the bodies of complex animals. 



Right up through the invertebrates and vertebrates, 

 with the curious .exception of the insect, spider, 

 shrimps, and millepedes, cilia occur in some part or 

 other of the internal organs. Even in ourselves the 

 cavities of the nose and windpipe, of the brain and 

 spinal cord, are lined with these vibrating rods, which 

 bear witness to a community of substance which links 

 us with the animalcules themselves. 



As the organs of movement, whether displacing 

 a minute creature or sluicing a fluid inside a large 

 one, these cilia bear witness to the deep-seated cause 

 of movement. Their activity is innate. So long 

 as they are bathed by water or their natural medium, 

 their movement is only indirectly controlled by the 

 action of the body, or even by its presence. If de- 

 tached, as they frequently are, from the dying body 

 of spherical jelly-fish (fig. 2) that come drifting to our 

 shores in summer, their movement continues for a 

 time unchanged in strength or pace ; and while able 

 to survive severance from the body temporarily, they 

 are equally their own masters in the starting as in 

 the maintenance of that unresting beat. Small 

 wonder that organs so self-contained have been 

 treasured, and that scope for their energy is found 

 in highest and lowliest alike. 



Yet all movement partakes of this mysterious, 



