TRACHEAL RESPIRATION 



127 



also of thoracic segments. As far as I know expiration is 

 always active, while the resting position brought about by the 

 elasticity of the integuments 

 and tracheal walls is nor- 

 mally the inspiratory. Re- 

 spiratory pauses in the 

 position of rest are not infre- 

 quent. The respiratory 

 movements affect also the 

 air sacs at a distance by the 

 transfer of blood, and in this 

 way even some ventilation 

 of the legs can be brought 

 about. Brocher (1920) de- 

 scribes the tracheal arrange- 



B C P 



Fig. 72. Diagram showing the part 

 played by the large air-sacs in the 

 abdomen of Lucilia during the growth 

 changes in the adult fly. A, fly just 

 emerged. B, after 5 minutes; gut filled 

 with air, distending abdomen. C, after 

 10 hours; gut collapsed, air-sacs dis- 

 tended. D, fully fed for 6 days; air-sacs 

 collapsed again while ovaries and fat 

 body fill abdomen, a air-sacs, b gut, 

 c ovaries, d fat body. (Evans.) 



ment in the legs of the but- 

 terfly Sphinx convolvuli. There are narrow air-sacs separating 

 the muscles of the femur and separating also a dorsal from a 



ventral lacuna in which the 

 blood is flowing and the sep- 

 aration is continued right 

 down the leg, as illustrated 

 in Fig. 73. In such a case 

 respiratory movements will 

 at the same time further the 

 blood flow and produce 

 some ventilation. 



In experiments on grass- 

 hoppers, Krogh (1913) found 

 that the oxygen in the tibial 

 tracheae was fairly high 

 (16%) when the animals 

 were quiet, but became re- 

 duced to 5% when they were 

 tired out by chasing them 



Fig. 73. Cross section of tibia of , r^, . , 



Sphinx, a and b, blood lacunae; 5, air about - * h ? ventilation, 



space. (Brocher.) which could amount to be- 



