34 C. SASAKI. 



a curious plienomenon to observe. On account of the tougb yet brittle 

 nature of the chitinous puparium, it breaks open easily when certain 

 forces are applied. The puparium (PI. Vljßg.lS^hreaks invariably 

 at its anterior end, and the lines of breakage are in two directions — 

 one longitudinally in the direction of c d., and the other transversely 

 in the direction of a h., so that the anterior portion above the fifth 

 segment is divided into two pieces (PL VI, fig. 13 a, h). The transverse 

 line of breakage ( PL VI, fig. 12 ah ) occurs at the junction of the 

 fourth ( 4 ) and fifth ( 5 ) segments of the puparium, of which the latter 

 is firmly attached to the body of the contained pupa (PL VI, fig. 14 c) 

 by the chitinous tube or spine (PL VI, fig. 14 e) provided on the sum- 

 mit of the top-shaped bodies on the anterior corners of the thorax. 

 The line of the longitudinal fracture (PL VI, fig. 12 c cV) divides the 

 part of the puparium in front of the transverse fracture into two bi- 

 laterally symmetrical halves (PL VI, fig. 13 a, h). Every specimen of 

 the puparium always breaks open in this way. Now the questions 

 arise : how do all the puparium break open in exactly the same mode, 

 and how does the newly hatched fly, which is perfectly helpless, get 

 above the ground? These are explained by a simple mechanical 

 process which the young flies perform. In escaping from the pupa- 

 rium, the fly, in a most strange fashion, protrudes a curious air bladder 

 (PL VI, fig. 14 f) from the oval space (P/. VI, fig. loa) on the front 

 edge of its head between the compound eyes This oval space is 

 membranous marked with a transverse line in the middle, and sur- 

 rounded by a dark line. Both the transverse and the circumferential 

 lines are due to the portion of the membranous space being folded 

 into the interior of the head, so that when the air has fully expanded 

 this space, no trace of these lines is seen. This becomes clearer by 

 looking at a section of the head shown in (PL VI. fig. IG) in wdiich a a' 

 are the dark marginal, and c, the central transverse lines. The air-sac 



