272 ' INSECTS AT HOME. 



dusted with fine sand, the force of the expelled vvater can he at 

 once measured by the displacement of the sand If the vessel 

 be a deep one, no such proof of the propelling power can be 

 seen, and the creature darts through the water as if impelled 

 by some magic power. The reader may perliaps remember 

 that a ' direct action ' movement has lately beea applied to 

 steamboats, the principle having been avowedly borrowed from 

 this very creature. 



There is very little change in form or habits between the 

 larva and the pupa. Towards the end of the larval existence, 

 a sort of longitudinal hump makes its appearance on the upper 

 part of the thorax, and, when the last larval skin is thrown off, 

 this hump is seen to consist of the future wings, which are at 

 present thick, narrow and small, their tips only reaching about 

 one quarter of the length of the abdomen. The mask retains 

 its place and office, but the head is much larger and broader, 

 and the splendid eyes of the perfect insect begin to shine 

 under their covering. 



It is quite as voracious in the pupal as in the larval stage of 

 existence. One of my own specimens has just seized with its 

 raask the larva of a Whirlwig Beetle which had been unlucky 

 enough to come within reach. The whole proceeding was very 

 much like that of the toad when catching insects. The mask 

 flashed out so rapidly that its movements were scarcely visible, 

 and in a moment the unfortunate larva had been grasped 

 by the middle and held against the cruel jaws. So rapid, 

 indeed, was the movement, that it looked very much as 

 if the larva had intentionally darted into its destroyer's 

 mouth. 



One of these insects made a rather absurd mistake. It saw 

 a detached leg of a Dyticus which was floating on the surface, 

 shot itself immediately under it, and seized the leg in passing. 

 It soon discovered its error ; and, after trying in vain to eat 

 the hard-shelled limb, jerked it away as if in anger. I have 

 noticed that in seizing its prey the Dragon-fly larva prefers, 

 like the shark, to get below it, and to make an upAvard stroke 

 with its armed mask. 



A still stronger proof of voracity was also given. I had 

 taken a larva of the Acilius, one of the Water Beetles, which 

 is closely allied to the Dyticus described on page 59. It is 



