66 MICROSCOPIC ILLUSTRATIONS. 



of its own size, while it is itself the prey of all kinds of 

 water-beetles and the larger larvae. 



It feeds on the larvae of the smaller kinds of tipulae, or 

 crane flies, as well as on aquatic vegetables. Short 

 pieces of grass, &c. are frequently seen in the alimentary 

 canal, when examined under the microscope during the 

 spring season. For this reason, and also on account of 

 the sharpness of its claws, it should not be kept with any 

 of the family of the Characese, intended to exhibit the cir- 

 culation (cyclosis) of the sap, inasmuch as it pierces the 

 cellules whilst creeping up the stems, and thus destroys 

 the plants. 



When it is intended to collect this larva, a mild calm 

 day should be chosen ; for if there be any cold wind, it 

 retreats into the mud at the bottom of the water. It may 

 be easily taken with a collecting net, such as is described 

 in the preceding chapter. This must be introduced 

 among the grasses and water-plants to which they attach 

 themselves. Having carefully done this on that side the 

 pond which is most exposed to the sun's rays, and drawn 

 it among the floating duck-weed, many hundreds may 

 often be collected at a single draught. 



These larvae may be kept alive, for many weeks to- 

 gether, in a glass vase of water, with a little duck-weed 

 floating on its surface ; and will be ready to be applied 

 to the microscope whenever required. 



The rapidity with which it moves is truly astonishing. 

 Besides its six legs, it employs the six double paddles at- 

 tached diagonally to the serpentine vessels on each side of 



