MAY-FLIES AND THEIR NEIGHBOURS 21 r 



remains, and, remarkable to say, becomes of greatei 

 dimensions than is usual, the stomach forming a 

 capacious sac. 



The older naturalists observed what graceful 

 balloon-like movements the " dancing May-flies " 

 possessed, but it is only of recent date that this 

 buoyancy has been satisfactorily explained. It 

 has now been found that their movements ca se 

 air to enter at the mouth which distends the 

 stomach sac, the orifices of which are then closed, 

 the result being that each insect becomes a living 

 balloon. 



The earlier life of the May-fly is somewhat 

 haphazard, for the eggs are committed to the 

 water in lumps without care or foresight on the 

 part of the parents. As a rule these egg-clusters 

 separate rapidly and the eggs sink broadcast to 

 the mud below, though some species of the flies 

 creep down into the water and deposit their eggs 

 carefully under stones and in other safe situations. 

 The eggs often remain until perhaps February or 

 March of the next year before hatching. When 

 the larva emerges it has no respiratory system, 

 but gills soon begin to appear, and growth seems 

 to take place but slowly. After moulting its skin 

 perhaps some twenty times each moult making 

 it differ in appearance within the period of its 

 one, two, or three years' growth, according to the 



