ciuA. 173 



is most entertaining. Some propel themselves 

 directly forward, with a velocity which ap- 

 pears, when thus highly magnified, like that 

 of an arrow, so that the eye can scarcely fol- 

 low their movements ; whilst others drag their 

 bodies slowly along, like the leech. Some 

 make a fixed point of some portion of the 

 body, and revolve round it with great rapidity ; 

 whilst others scarcely present any appearance 

 of animal m.otion. Some move forwards by 

 a uniform series of gentle undulations or vibra- 

 tions ; whilst others seem to perform consecu- 

 tive leaps of no small extent compared with 

 the size of their bodies. In short, there is no 

 kind of movement which is not practised by 

 these animalculse : they have evidently the 

 power of steering clear of obstacles in their 

 course, and of avoiding each other when swim- 

 ming in close proximity. By what kind of 

 sensibility the wonderful precision and accu- 

 racy of their movements is guided is yet very 

 doubtful. The general surface, in those whose 

 bodies are not inclosed in a firm envelope, ap- 

 pears very susceptible of impressions. No 

 organs of special sensation, however, can be 

 detected, except certain red spots observable 



