2 6o ANIMAL LIFE 



those of the other gnats and midges, this black-fly pupa 

 does not float and cannot leave its nest, yet the flies 

 pass the gauntlet of the stream. They emerge safely 

 in thousands, and may be seen clinging to weeds on 

 the borders of the stream. The method of hatching is 

 singular. The pupa not only stores air in its breath- 

 ing tubes by diffusion, but actually distends its skin 

 therewith, and so separates it from that of the fly. 

 Ultimately the pupal envelope bursts and the fly 

 emerges, still with intricately contorted appendages, 

 and surrounded by a bubble that clings to its hairy 

 covering. In a moment it rises glistening to the surface, 

 where the bubble bursts. Its legs spread out with 

 almost explosive suddenness ; with these it easily runs 

 on the surface-film, climbs up the nearest support, and 

 then expands and dries its wings. 



The Drone-fly (Eristalis). In great contrast with 

 these remarkable adaptations of midge -larvae and 

 pupae to life in flowing water, are those shown by 

 the drone-flies, and some daddy-longlegs in their 

 earlier stage of development. The larvae of these 

 flies are elongate, whitish, worm-like maggots, with a 

 long rat-like tail. Their breathing tubes are well 

 developed, and open to the surface at the tip of the 

 tail. By the aid of a telescopic arrangement this tail 

 can be protruded to a length of some inches, so that 

 while the larva is buried deep in mud, its breathing 

 tubes can reach up to the surface of the water, break 

 the film by the point or hooks of the tail and acquire 

 a supply of fresh air. This arrangement is most- highly 



