NEUKOPTERA. 



133 



abdomen from those of the pupa -while the wings are 

 four small clouded appendages, little larger than the 

 wing cases of the pupa. 



The young fly stands Fig. 46. 



still in the position al- 

 ready described ; and as 

 we watch it the wings 

 appear a little and a 

 little larger, until there 

 can be no doubt of 

 their increase in size. 

 Suddenly the insect 

 moves, quitting the 

 pupa-case it walks ra- 

 pidly up the stalk 

 to which that clings. 

 Whilst this action con- 

 tinues, and for a little 

 while after it ceases, 

 the abdomen appears to 

 become inflated. The 

 fly then becomes quiet, 

 but we observe the in- 

 flation of the abdomen to be subsiding and the wings to be 

 so quickly increasing in size that the actual motion is ap- 

 parent, we see them growing. This continues until the 

 abdomen is restored to its former slender shape, when the 

 wings cease to expand ; the walk is then repeated, and 

 with the same result, until the four wings have arrived 

 at their full size (fig. 47). The explanation of this 

 proceeding probably is that by the exercise of walking 

 respiration is quickened, and the air vessels in the abdo- 

 men are filled with air, which is expelled thence possibly 

 by a voluntary muscular contraction into the wings, and 



