WERNER MARCHAND 161 



Since the puparium is unrolled from the head, the compound eyes 

 are soon exposed to view, so that the sex of the fly may be distinguished. 

 The appendages, antennae, palpi, and mouth-parts are dimly visible. 

 The head appendages are freed primarily by the spasmodic wriggling 

 of the abdomen, but the labellum, which is seen to become turgid and 

 flaccid in turn by the injection of air into, and withdrawal of air 

 from, the "extensive tracheal sacs which lie in the cavities," and the 

 erectile stomal disk through the pressure downwards against the walls 

 of the puparium, assist also in the process. That these head ap- 

 pendages assist effectually in the emergence is evident from the 

 lines of cleavage in the enveloping membranes. 



The puparium splits on the median line of the thorax; simul- 

 taneously the hood enveloping the head drops by a sternal hinge. 

 The labellum can be seen still pressing upon the interior of the hood 

 as the head emerges. In a minute the wings are rent from their 

 envelopes by the sturdy pressure of the legs, which have slid out of 

 their sheaths simultaneously with the cleavage of the thorax. The 

 legs directly assume their normal position, and the fly walks forth 

 bodily, spreading its plicated wings. The liberated wings show a 

 clear expanse of unwrinkled membrane which at first is soft in texture 

 and clear lead-colored throughout. Finally the inflated abdomen 

 appears in the dorsal slit, and at once is drawn clear of the encumber- 

 ing puparium. 



The time from the appearance of the head to the evacuation of the 

 puparium requires less than two minutes. This time is increased a 

 minute or two whenever the wing sticks to the lining of the puparium, 

 resulting usually in a torn wing. 



Directly after emergence the wings are shorter than the body, but, 

 constantly vibrating, they gradually lengthen, whereupon they be- 

 come hardened and prepared for flight. The fly does not spend any 

 time preening itself, as is the case with some of the Muscidae at this 

 stage. The time prior to flight is spent, however, in a clearing 

 process. This begins with a copious discharge of meconium within 

 three to five minutes after emerging. At first the defecation is per- 

 formed at least five times per minute, then once per minute for a 

 period of twelve minutes. At the end of this time the excretions be- 

 come more watery in character. In the meantune the fly walks 



