GRACEFUL EVOLUTIONS. 91 



bright sunshine the splendid iridescence of colouring 

 caused by the action of their cilia to the greatest ad- 

 vantage. As they wheel onwards, rising and falling 

 at pleasure, and creating in their course the glory by 

 which they are encircled, they seem indeed 



" gay creatures of the element 



That in the colours of the rainbow live." 



The variety of their evolutions constitutes one of 

 their principal charms. Sometimes they will ascend 

 from the bottom of the jar to the surface of the water 

 with a slow and regular movement, resembling that 

 of a balloon, and descend at the same rate of progres- 

 sion. Again, they will rise more rapidly, and turning 

 their mouth downwards descend with equal rapidity. 

 At other times, without rising or falling, they will 

 revolve on the transverse axis of their body then, 

 abandoning all these modes of progression, they will 

 revolve on their longitudinal axis, holding the body 

 vertical, and in this position twirl round and round 

 the glass like graceful waltzers. When the move- 

 ments of the animal are thus varied, how great must 

 be the variety of motion in the cilia by which the 

 body is propelled ! Never for more than a second or 

 two do the cilia cease to vibrate. Even then it is 

 not a total suspension, but a slower and alternant 

 action that is exhibited ; the cilia on one or two con- 

 tiguous bands remain stationary, while the adjacent 

 ones on either side are in motion then those which 

 have been still begin to play, and those that were 

 previously moving remain still : no regular succession 

 of procedure is observable, but some portion of the 



