VIII. B, 3 Mitzmain: Biology of Tdbanus striatus Fabricus 213 



eye, the epidermis of the fly separating from its connective-tissue 

 fastening of the puparium can easily be seen. This action re- 

 sembles strikingly a wave of water moving between the walls of 

 the puparium and the epidermis of the fly. It may be considered 

 as the movements of a semiliquid layer between the fly and its 

 puparium. Another movement, which can be observed within a 

 few minutes after that previously described, is the momentary 

 contraction and expansion of the sides of the abdomen between 

 the two lateral ridges. This too, no doubt, is effective in tearing 

 the connective-tissue lining to facilitate emergence. A few min- 

 utes later the anal end of the abdomen is torn loose from its 

 fastening, and emergence of the fly begins. 



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 pri- 

 marily 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 ''ex- 

 tensive tracheal sacs which lie in its cavities," and the erectile 

 stomal disk through its pressure downward against the walls 

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

 appendages 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 in- 

 terior of the hood as the head emerges. Within 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 un- 

 wrinkled 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 encumbering 

 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 



