ORIGIN OF THE SILVER EEL. 49 



upon it the same as on land ; this it is en- 

 abled to do by a membrane upon each foot, 

 which confines as much air as balances its 

 weight, and this membrane, when reversed, 

 forms a sucker by which the insect can cling 

 to smooth stones. This is the only amphi- 

 bious fly that has a compound nature, breed- 

 ing on land and going to the water, in the 

 same way as the eel beetle. This being the 

 difference : in the case of the eel beetle, a 

 neuter is produced and sent to the water, 

 but this fly goes itself. Of the second class 

 of amphibious flies with a mixed nature, 

 there are many more than I can now de- 

 scribe. They are nearly one year in the 

 water in different forms, then rise out of it, 

 spawn, fly about the rest of the summer, 

 and die on the approach of cold weather. 



