282 EVENINGS AT THE MICKOSCOPE. 



slielly case, as a Wheel-bearer, a "Water-flea, or au In- 

 sect, and soon devour every particle of soft flesh, clean- 

 ing 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 satisfac- 

 torily defining 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, some- 

 what like the body of a wine-glass, without any foot, but 

 bearing many flat sword-shaped processes, which, pro- 

 ceedins: from the breast, commonlv lie flat on each side, 

 down the body, the points projecting below. These are 

 evidently stift" and highly elastic, and their use is mani- 

 fest to any one who sees the creature in active iiiotion. 

 It swims with a rapid gliding progress, head foremost, 

 but at almost every moment 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 tran- 

 sition. The organs by which these jumps are efi'ected 

 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 con- 

 sider that the creature is jerked often four or five times 

 its own length, through so dense a fluid, we shall per- 

 ceive how strong the muscular action must be which 

 moves the lever-like spines. The creature is thrown 

 irreo-ularly, often with the side foremost, or the back, 

 or made to perform a somersault in the act. It is prob- 

 ably a sensitiveness to danger or annoyance that 

 prompts these violent leaps ; at least, it frequently 

 performs them, after a momentary examination of any 

 floatino- matter with which its course brmgs it into 

 contact. 



