130 RESPIRATORY MECHANISMS 



electromyograms) to about 32°, and that regular flight is not 

 possible until this temperature is reached. The violent 

 "pumping" ventilation provides the oxygen for this heat 

 production. 



During the flight itself an even larger ventilation must be 

 necessary, but the mechanism of this ventilation differs greatly 

 from one insect to another. Very instructive observations 

 and experiments were made by Fraenkel (1932), who pro- 

 voked flight movements reflexly in insects suitably fixed for 

 observation. 



In Wasps (Vespa orientalis) there is an increase of 5 to 10 

 times in amplitude of the abdominal respiratory movements, 

 while the rhythm remains the same, but complete suppression 

 of the abdominal ventilation does not prevent the flight of 

 the wasp. 



In the large grasshopper Chistocerca gregaria the abdominal 

 ventilation often ceases completely for a couple of seconds 

 when flight begins, but starts again with a much increased 

 rhythm and slightly increased amplitude. 



In Libellula the respiration goes on as during rest, but in the 

 large butterflies {Sphinx, Deilephila), which practically do not 

 ventilate during rest, respiratory movements with a rhythm of 

 30-40 become visible during flight. 



In the cockchafer, which shows a greatly increased ventila- 

 tion as a preparation for flight, this stops completely the mo- 

 ment actual flight begins. During a prolonged flight ab- 

 dominal ventilation may start again after 2 to 3 minutes. 



It is evident that the visible ventilation during flight cannot 

 in any of the species studied be adequate to deal with the 

 enormous increases in metabolism. The conclusion appears 

 inevitable that the flight movements must themselves bring 

 about the necessary ventilation of the flight muscles. Brocher 

 (1920) has given a description of these muscles in the butterfly 

 Sphinx convolvuli from which it appears that their rhythmic 

 activity might act upon the air sacs surrounding the muscle 

 bundles and perhaps upon the small tracheae penetrating 

 them so as to produce the necessary ventilation, but a more 



