146 



SYSTEMATIC ZOOLOGY. 



which are in constant motion, and when the animal 



casts itself loose these serve like 

 so many oars to propel it through 

 the water. At the larger end of 

 the body these hair-like organs 

 become much larger, and they 

 are here arranged in a spiral. 

 The effect of their constant mo- 

 tion is to create a minute whirl- 

 pool in the water, the centre of 

 which is in an opening in the 

 larger end. This may be com- 

 pared to a mouth. The water 

 brings with it minute particles 

 suitable for food, and these pass 

 through the mouth into a cavity 

 comparable to a gullet, from which 

 they pass into the central part of 

 the cell, where they are digested. 

 Then the indigestible portions are 

 at last passed out from the body 

 at a fixed point, the functional 



V6Ilt - The lar S 6 cllia alwa ^ S 

 m Ve in a ^ and rhythmic 



manner-a fact which would im- 



FIG. 2.-Diagram of a Proto- 

 c Z ,fa n r g e b ci.ia aroTd 



nerve b rig 9: w> nucleus; nr ' ply that they were connected and 



controlled in some manner in their 



action; and high microscopic powers show at their bases 

 a cord of somewhat denser material which takes the place 

 of a central nervous system. If this be cut, the cilia no 

 longer work in harmony. Finally, all animals, in doing 

 work, produce nitrogenous waste, which must be got rid 

 of by means of kidneys. In the form figured the kidneys 



