140 DROPS OF WATER. 



wonderful construction, I have spoken in the in- 

 troductory chapter ; by their means a whirlpool 

 is caused in the water, smaller creatures are 



drawn into it, and swallowed bv the mouth : this 



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apparatus forms, also, their means of locomotion, 

 and in many genera the swimming is very rapid. 

 These delicate cilia can be withdrawn at pleasure, 

 and covered securely by the rest of the body. 

 The gullet contains a set of sharp teeth, which 

 grind down the food very rapidly, and which may 



be seen constantlv in action whilst the animalcule 



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is feeding. The foot or tail, as it is sometimes 

 termed is in many genera of very wonderful con- 

 struction ; it is formed so as to enable the little 

 creature to make it long or short at pleasure, by 

 one part sliding within another, on the same con- 



