262 PEESH-WATEE AQUAEIA. 



the bristles wHcli guard the orifice open in a star-like fashion, 

 admit the air, and close again, to prevent the ingress of the 

 water as the larva, with its extraordinary motion, dives down 

 again to the bottom of the pond, ditch, or tub. There are 

 some curious bristle-like fins attached to the last segment of 

 the body, which seem to assist it in swimming and sustaining 

 itself near the surface of the water during the act of respira- 

 tion. These larvae are useful in helping to cleanse the water 

 in which they live by devoui-ing various decaying matters which 

 they find there. The jaws of these creatures are fringed with 

 bristles in such a way that they are able to cause a small 

 current of water to set in towards the mouth, and so suitable 

 food is brought within the insect's 

 reach. If some of these larvse are 

 kept in a plate in which there is a 

 little pond-water, this very inte- 

 resting manner of feeding may be 

 ""^'^^ W^ \ plainly seen through an ordinary 



'^ magnifying-glass. These creatures 



swim by alternately straightening 

 ^'"op'U^'^^^mmSnXI ^d bending their bodies. They 

 (CuLEx ciLiABis). never seem to make any journeys, 



except those between the bottom 

 of the water and its surface. If one should go, during 

 warm and sunny weather, cautiously to the side of some old 

 tub or butt full of water, he wUl most likely see several of 

 these larvse busily taking in fresh supplies of air; but directly 

 they notice any movement upon the observer's part, they, 

 will wriggle and jerk their way down to the bottom out 

 of sight. They, may be easily captured by placing under 

 them, as they descend, a small hand-net made of very fine 

 musliu. These creatures are useful for feeding small fish and 

 other aquatic animals upon. 



Before the larvaa of Gnats enter their pupalhood they 

 change their skins at least three times. The pupa is in 

 appearance very different to the larva. It seems to be top- 

 heavy, on account of what may be called its head. This head 

 is enormous (Pig. 160), in proportion to the size of the body. 



