36 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



really lost or not should be investigated further. Kellogg 

 points out that in this group the very unusual condition ob- 

 tains of the wings becoming fully developed within the pupa. 

 The fully developed wings lie in the pupal case folded both longi- 

 tudinally and transversely, and only need to unfold to be ready to 

 carry the fly into the safe air. It is this folding which produces the 

 secondary veining of the wings characteristic of the family, this vein- 

 ing being simply the persisting creases and lines of the folding. 



As already stated, in the Cyclorrhapha the escape of the 

 imago is effected by means of the ptilinum or frontal bladder. 

 This bladder is situated above the roots of the antenna? and is 

 only inflatable in the immature fly. Later it is permanently 

 retracted or disappears altogether. When the fly is ready to 

 leave the puparium the bladder is alternately inflated and re- 

 tracted until the front portion of the puparium, which has 

 lines of weakness for this purpose, is forced off. Some indi- 

 cation of the pressure thus exerted is obtained from some ex- 

 periments made by Michl with pupae of Muscina stabulans 

 Fallen. 1 When the fly which was about to emerge had burst 

 off the lid of the puparium its escape was prevented by fast- 

 ening a strip of paper across the opening, the puparium being 

 fixed immovably. The fly would then endeavor, by inflating 

 its ptilinum, to remove or perforate the obstacle. So great was 

 the pressure exerted that in one case out of eleven the frontal 

 bladder was ruptured. 



The earlier authors supposed that the ptilinum is inflated 

 with air, but Joly, 2 and independently Reissig, 3 showed that 

 it is filled with blood forced from the body into the head. 

 Reissig aptly compares the action to that of an hydraulic press. 

 Through what channels the blood is forced forward has not 

 been determined. Reissig suggested that special vessels, sup- 

 plied with valves, existed. Weismann thought that it was 

 accomplished by the dorsal vessel, as this is the main channel 

 through which the blood is carried forward from the body- 

 cavity. 4 Joly already showed that the ptilinum was inflated 

 by violent contraction of the abdomen, thus forcing forward 



1 Einiges iiber das sogenannte Ptilinum der schizophoren Dipteren. 

 Mitt, naturwiss. Ver. Univ. Wien., vol. 8, pp. 85-89 (1910). 



"Recherches . . . sur les oestrides, etc. Ann. Sci. phys. et nat., 

 agric. et indust. de Lyon, vol. 9 (1846), p. 204. 



3 Ueber das Herauskommen der Tachinen aus ihren Tonnchen und 

 aus dicht verschlossenen Orten, an welchen diese oft sich befinden. 

 Archiv f. Naturgesch., Jahrg. 21, vol. 1 (1855), pp. 189-196. 



'Die Entwicklung der Dipteren, p. 227 (1864), reprint from Zeitschr. 

 wiss, Zool., vols. 13 and 14. 



