28 DROPS OF WATER. 



orifice by their rapid movement, which creates a 

 current in the water, but the same action propels 

 the body with wonderful speed, so that the eye 

 can scarcely follow it. These cilia, when in mo- 

 tion, have the appearance, to the eye of the spec- 

 tator, of a rapidly-revolving wheel, and this ex- 

 traordinary effect is produced in the following 

 way. Each of these little thread-like members 

 has a rotatory motion, the point describing part' 

 of a large circle, and the base (which is seated 

 on a bulb) part of a small one ; this motion, when 

 all are seen in action at once, gives the appear- 

 ance of a turning wheel, because the apparent 

 revolution of the whole takes place in the same 

 time as the real rotation of a single one. I 

 know nothing more wonderful than this forma- 



