WHEEL-BEARERS 259 



revolution. Is not this a charming sight? Round and 

 round go the wheels, forming two perfect crowns, which 

 rotate with uninterrupted and unceasing course, smooth 

 and regular, which we can compare with nothing else 

 than the crown wheel of a watch, if allowed to run down. 



Now these are examples of ciliary action. Though at 

 first it is almost impossible to persuade one's self that 

 there is not an actual rotation of parts, yet this- is only 

 an illusion, as I have already explained. The waves 

 alone move, the cilia themselves retaining their position 

 unchanged except that they alternately bend and erect 

 themselves. It may assist your idea of this motion to 

 advert to a field of corn, over which a smart breeze is 

 blowing. You see that waves chase each other across the 

 field; but your reason, and indeed your observation, tells 

 you that this appearance is produced entirely by the al- 

 ternate bending and rising of the ears of corn, which are 

 of course stationary. 



The beauty and wonderfulness of these ciliary wheels 

 are so striking, especially when one sees them for the 

 first time, that for a while we see nothing else: we can- 

 not take our eye off from them. But when you have a 

 little satisfied your sense of seeing, you may examine 

 other points of interest in this charming little animal. 



The cilia are remarkably stout and long in this genus, 

 but on the middle lobe of the front there are other 

 processes of the same character; but still stouter. These 

 too are not properly vibratile, at least they do not make 

 circular wheels: ordinarily they project like stiff erect 

 bristles, or converge toward each other. 



Between the two middle spines the shell is cut into 

 a deep notch, out of which protrudes, when the wheels 



