PHllYGANE^. 24-7 



nature collect round themselves, some, parts 

 of plants, or small sticks ; some, gravel ; and 

 some, even shell fish. They spin themselves 

 a sort of case of silk from their bodies, and 

 by a gluten, that exudes from this case, ce- 

 ment their materials together. They feed 

 upon aquatic plants, and sometimes upon in- 

 sects, protruding only their head and legs 

 from the case. When about to undergo 

 transmutation, they quit their cases, rise to 

 the surface, and wait for this process of na- 

 ture in the air; but some species fix them- 

 selves on plants or stones : they burst the 

 skin of the larvae, and appear perfect animals, 

 male and female, fitted for the office of re- 

 production. In the early spring, the species 

 which are called green tails, from the colour 

 of the bags of eggs in the female, appear in 

 the warm gleams of sunshine that happen in 

 cloudy days, and they then cover the face of 

 the water, and are greedily seized on by the 

 fish. As the season advances they appear 

 principally in the morning and evening. In 

 the heat of summer the phryganeae are almost 

 nocturnal flies, and seem to have the habits 

 11 4 



