BACKBONELESS ANIMALS WHICH BREATHE IN AIR 441 



to time at the surface for the purpose of taking in air, but the 

 details have not yet been made out. 



Fig. 559. The Drone- Fly {Eristalis tenax] and its larva, the Rat-tailed Maggot 



The larvae of a great many Two- winged Insects (Diptera) live 

 in water, and in many cases come to the surface to breathe air. 

 It is then usual to find a breathing- tube at or near one end of the 



