WHEEL- BEARERS. 245 



the soft internal parts by decay, and by the efforts of 

 those little scavengers, the smaller species of infusorial 

 animalcules. These quickly find their way into the interior 

 of any dead animal with a shelly case, as a Wheel-bearer, 

 a Water-flea, or an Insect, and soon devour every particle 

 of soft flesh, cleaning out the case in the most tidy 

 'manner. 



Here is a tiny subject which will test your powers of 

 observation, and possibly your patience, in satisfactorily 

 denning its structure, partly on account of its swift motion 

 and irregular leaps, and partly on account of its extreme 

 transparency. It is a crystalline cup, somewhat like the 

 body of a wine-glass, without any foot, but bearing many 

 flat sword- shaped processes, which, proceeding from the 

 breast, commonly lie flat on each side, down the body, 

 the points projecting below. These are evidently stiff and 

 highly elastic, and their use is manifest to any one who 

 sees the creature in active motion. It swims with a rapid 

 gliding progress, head foremost, but at almost every mo- 

 ment it makes a sudden forcible jerk or" leap backwards or 

 to one side, and that so quickly that the eye often cannot 

 follow it in the transition. The organs by which these 

 jumps are effected are the long breast- spines, which are 

 suddenly thrown out in various directions ; and they may 

 frequently be seen extended the instant after a leap. When 

 we consider that the creature is jerked often four or five 

 times its own length, through so dense a fluid, we shall 

 perceive how strong the muscular action must be which 

 moves the lever-like spines. The creature is thrown irre- 

 gularly, often with the side foremost, or the back, or made 

 to perform a somersault in the act. It is probably a sensi- 

 tiveness to danger or annoyance that prompts these violent 

 leaps ; at least, it frequently performs them, after a 

 momentary examination of any floating matter with which 

 its course brings it into contact. 



The rotatory organs, the source of the common gliding 



