GNATS 21 



together, and left to float upon the water as a raft about i inch 

 in length. The individual eggs are roughly cigar shaped, and 

 stand upright side by side ; the upper end is more pointed than 

 the lower, which is provided with a lid through which the larva 

 eventually emerges into the water, head first. The eggs are so 

 closely packed together that the water cannot penetrate between 

 them, even if they be forcibly submerged ; and they are so 

 buoyant that they always float on the surface in the correct posi- 

 tion. The eggs round the margin of the raft stand a little higher 

 than the more central, and these act as a bulwark. Thus the eggs 

 are in reality entirely above the water and completely surrounded 

 by air, so that respiration takes place freely through the egg-shell. 

 The larvae which emerge are commonly known as " wrigglers " 

 from their method of locomotion. When undisturbed they live 

 at the surface of the water, hanging head downwards. If alarmed 

 they dive to the bottom, travelling with a peculiar wriggling, 

 lashing movement of the body. At this stage the animal has a 

 large head and thorax and a rather tapering, more slender abdomen 

 of ten segments. The head bears a pair of compound eyes, a 

 pair of short antennae, and jaws which are provided with numerous 

 vibratile bristles. These bristles are employed in sweeping 

 minute particles of food into the downwardly directed mouth, 

 and also at times to row the animal along without alteration 

 of the bodily attitude. The thorax has no limbs, neither legs 

 nor wings ; but the fact that it is composed of the usual number 

 of segments is indicated by three pairs of tufts of conspicuous 

 bristles one behind the other. The segments of the abdomen 

 are clearly marked off by constricting grooves ; the first seven 

 present no remarkable features, each being provided with a pair 

 of bristly tufts. From the eighth, however, there projects a 

 peculiar and very conspicuous organ the respiratory siphon. 

 This is a cylindrical structure enclosing two air-tubes which 

 open at its extremity and pass along the whole length of the 

 body to supply all parts with air. In the resting position the 

 tip of the siphon is thrust through the surface of the water, so 

 that its cavities are in free communication with the air above. 

 The ninth segment is small ; the tenth larger, and furnished 

 with strong bristle tufts of which the ventral serves as a pro- 



