YOUNG THINGS 7 



spent the Winter in hiding, lays two or three hundred eggs 

 on an early morning in Spring. She does so in such a way 

 that they adhere to form a minute raft about a quarter of 

 an inch across which floats on the surface of the pool, and 

 can neither be submerged nor wetted. Each egg is some- 

 what cigar-shaped, with the upper end pointed, and the 

 lower end with a lid, which opens to let the larva out into 

 the water. The larva speeds most of its time hanging 

 head downwards from the surface-film, through which it 

 protrudes a respiratory air-tube. Very delicate hair-like 

 organs sweep microscopic particles into the mouth. If you 

 push the larva below the surface it sinks to the bottom, 

 but it can jerk itself up again tail foremost. There are 

 no limbs, but the tail part can strike the water vigorously, 

 and there are numerous tufts of bristles on the sides of 

 the body. 



The larva feeds and grows and moults, and after 

 three or four moults it is full-grown almost half an inch 

 in length. It then passes into a pupa-stage, very markedly 

 contrasted with the larva, and within the pupa-skin the 

 transformation from larval to adult structure, which has 

 been in progress for some time, is accomplished. The 

 pupa has a strange shape, with a big " head-end " that 

 seems all out of proportion, and with a paired paddle at 

 the posterior end. It rests at the surface, head upwards, 

 breathing by two horn-like or trumpet-like tubes. It 

 does not eat at all, and when it is alarmed it has to swim 

 forcibly downwards, so buoyant is its body. After three 

 or four days of pupa-hood the cuticle splits along the back, 

 the limbs are pulled out of their sheaths, and the gnat 

 emerges, not without risk and difficulty. It rests for a 

 short time, standing on its own husk, and then flies off 

 into a very different world. The whole period of develop- 

 ment is about a month, and there may be many successive 



