TRACHEAL RESPIRATION 131 



detailed study extended to several species among the good 

 fliers is highly desirable. Portier (1933) ascribes to the wings 

 themselves in butterflies an important role in ventilation, but 

 it appears more likely that his experimental results are due to 

 interference with the circulation, which is of course of the 

 utmost importance in muscles working at the rate of metabo- 

 lism indicated above, even when it is not responsible for the 

 oxygen supply. 



The regulation of tracheal ventilation. The ventilation of 

 tracheae in insects is, like the ventilation of the lungs in higher 

 vertebrates, subject to a number of reflex influences, and it is 

 not at present possible to make out the relative importance of 

 chemical regulation and of reflex regulation, the more so as a 

 quantitative formulation of the problem has not so far been 

 attempted. 



J. Stahn (1929) counted the respiration rhythm in Dixippus 

 under the influence of varied atmospheres and found that even 

 low concentrations of C0 2 , from 0.2%, definitely increased the 

 frequency. It is known for a number of ventilating insects 

 (Krogh, 1913; Hazelhoff, 1926, and others) that they react by 

 increased ventilation to CO2 in the inspired air. 



Hazelhoff noted that while the spiracle reaction to CO2 in 

 the cockroach was instantaneous, the ventilation reaction took 

 a couple of minutes to develop and remained for several 

 minutes after the readmission of pure air, and this points 

 definitely to a chemical mechanism acting on the nerve centers. 



McGovran, who accurately measured the ventilation on 

 grasshoppers (Chortophaga, Dissosteira, and Arphia), found in- 

 creases up to 20 times the normal in 15% CO2, but failed to 

 detect any in 1%. 



The regular opening and closing of spiracles which causes 

 the ventilation to take place in a definite direction must 

 necessarily be governed from the central nervous system and 

 coupled with the ventilating movements. 



In some of the insects (Vespa, Macroglossum) in which the 

 visible respirations are increased during flight, Fraenkel found 



