210 SALMONIA. . 



all the aquatic insects found in this element, 

 and changing their skins at various times, 

 they emerge in their winged form the tyrants 

 of the insect generations in the air. The 

 gnats and tipulae have a similar existence. 

 The gnats, the female of which only is said 

 by De Geer to bite man, or suck human 

 blood, in Sweden, lays her eggs in a kind of 

 little boat or cocoon of her own spinning. 

 These eggs are hatched on the surface of 

 the water, and produce the larvae, which un- 

 dergo another change into peculiar nymphae, 

 which still retain the power of swimming 

 and moving, from which the perfect insect 

 is produced during the summer heat. The 

 flies which I mentioned to you in a former 

 conversation, under the name of the grannom, 

 or green tail, (see fig. 2,) are of the class 

 phryganece, which includes all those water 

 flies which have long antennae, and wings 

 something like those of moths, but usually 

 veined and without powder. The yellow 

 flies which you saw a short time since sport- 

 ing on the banks of the river, are of this 

 kind. The phryganeae (see fig. 1, 2, 3, 



