ON THE LIFE HISTORY OF UGIMYA. 



35 



is thickly covered with short strong setœ (PI. VI, fig. 16 h\ and it can 

 be either folded in or projected out of the head at will, simply by driv- 

 ing the air from the air-sacs in the head into the sacs in the thorax 

 and abdomen or by reversing this process. 



As has been said before, the contained fly is firmly attached to 

 the puparium or pupa case at the two points where the respiratory 

 tubes stick out on the fifth segment (PZ. VI, fig. 14 a a). These points 

 act as the fulcrum when the air-bladder is expanded to force open the 

 puparium. Again the air-bladder is not circular, but squarish in form, 

 so that when it is expanded, it touches the puparium only at two 

 points h h' (fig. 14). The greatest force is therefore applied at these 

 two points, and the tendency will be to split the part of the puparium, 

 in front of the 5th segment in the line c d fig. 12. The transverse 

 fracture naturally occurs at the junction of the 5th and 4th segments as 

 the body of the fly is firmly fixed to the former. These considerations 

 will explain why the puparium invariably breaks open in exactly the 

 same manner. 



By carefully listening, we may easily recognize the hatching out 

 of the fly (PI. VI, fig. 17 h) under ground by a peculiar cracking 

 sound produced at the time when the puparium is broken open by the 

 action of the temporary air-bladder. When the perfect fly (PI. VI, fig. 

 17 c c) has made its exit out of the puparium (PI. VI, fig. 17 a a') by 

 the process just described, its next step is to crawl up to the surface of 

 the ground. As the wings of the newly-hatched flies are folded up, 

 and their legs so soft that they are perfectly useless for locomotion, 

 they cannot use the ordinary means of reaching the surface against the 

 resistance of the earth which overlies them. This, however, they 

 easily perform by the alternate expansion and contraction of the air- 

 bladder of the head. They first project the air-bladder (P/. VI, fig. 

 17 e) upward into the overlying layer of earth, and then, expand 



