EPHEMEBAL FLIES. 129 



It is one of the most beautiful species of flies, and 

 undergoes five changes. At first the egg contains 

 its vital principle ; it conies forth a small caterpillar, 

 which is transformed into a chrysalis, then into a 

 nympha, and lastly into a fly, which deposits its 

 eggs upon the surface of the water, where the sun's 

 rays bring them to life. Each egg produces a little 

 red worm, which moves in a serpentine manner ; as 

 soon as the cold weather sets in, this little worm 

 makes for itself a shell, or lodging, where it passes 

 the winter; at the end of which it ceases to be a 

 worm, and enters into its third state, that of a 

 chrysalis. It then sleeps till spring, and gradually 

 becomes a beautiful nympha, or a sort of mummy, 

 something in the form of a fish. At the time of its 

 metamorphosis the nympha at first seems inactive 

 and lifeless; in six days the head appears, raising 

 itself gradually above the surface of the water ; the 

 body next disengages itself slowly and by degrees, 

 till at length the whole animal comes out of its 

 shell. The new-born fly remains for some minutes 

 motionless upon the water ; then gradually revives, 

 and feebly shakes its wings, then moves them 

 quicker and attempts first to walk, then to fly. As 

 these insects are all hatched nearly at the same 

 time, they are seen in swarms for a few hours 

 flitting and playing upon the surface of the water. 



