ii6 INJURIOUS AND USEFUL INSECTS 



perienced .observer. While studying the floating pupa with a 

 lens he will see a commotion in the object, and before he has 

 had time to realise what is going on, the fly is off and away. 

 Examination of the cast skin teaches us that the pupal skin 

 cracks lengthwise along the thorax, and that the fly emerges 



Fig. 64. — Female fly of Chironomus dursalis. X 8. 



here, drawing its head backwards, its legs upwards, and its 

 abdomen forwards to this one slit. The cast skin fills with 

 air as the body is withdrawn, and forms a float upon which the 

 fly can rest for a time if so disposed. By attentive examina- 

 tion the top of the back of the fly can be seen to protrude for 

 a minute or two just before the insect escapes, and I imagine 

 that at this time the legs, feelers, and other tight-fitting parts 

 are loosened from their sheaths. It is curious to see the fly, 



