xxn INSECTA : DIPTERA 337 



water surface, the body now becoming almost horizontal 

 (Fig. 259). 



The larval skin is not cast off, but hardens and remains as 

 a loose case, the pupal body within it only occupying 

 a quite small space at the head end. The pupa is enclosed 

 by a little silken cocoon, and it lies motionless within the 

 larval skin. After a few days the outer skin splits across 

 the thorax, usually just behind the first segment, and 

 then down the middle line for two segments and across 

 the fourth segment of the body, the big fly pushing open, 

 as it escapes, the little " cupboard doors " so formed. In 

 spite of its heavy body, the fly is able to stand on the 

 surface film of the water, and its hairiness prevents it 

 from getting wet as it emerges. After a short while the 

 wings unfold and stiffen, and then it flies away. The eyes 

 of this fly when first it emerges are wonderful to see in 

 their brilliancy. 



Practical Notes on Diptera Brachtcera 



1. Study the flies to be seen about the house, and try to dis- 

 tinguish the different species which are most common.! Obtain 

 a little " fly-blown " meat and watch the development of the 

 Blow-fly. 



2. Search the leaves of rose-trees, limes, sycamores, or any plants 

 infected with Aphides for the larvae of the Hover-fly. Separate 

 one and test its efficiency as an Aphis destroyer. Keep it until it 

 pupates and the fly emerges, making notes on the development. 

 Watch the flies in the garden hovering over the flowers, and learn 

 to distinguish them by their flight and colouring. 



3. Obtain some Drone-fly eggs or larvae from a manure-tank or 

 dirty rain-water tub, and keep them in a wide shallow jar of rain- 

 water, with plenty of decaying vegetation at the bottom. Watch 

 the movements of the rat-tailed maggots which hatch from the 

 egcs, drawing them to scale. Put one in shallow water first, then 

 add water to the vessel, and note the extension of the tail, and 

 sketch again to scale. Put the full-grown larva into a shallow 

 dish, with an earth bank rising above the water at one side, and 

 note the date of pupation and later the date of the emergence of 

 the fly. Jfake notes on the appearance and structure of the fly. 



' See Miall's Hoiise, Garden, and Field, chap. xix. 

 VOL. I Z 



