13 SUMMARY 14 Weibel and Taylor"s theory of symmorphosis predicts that the structural components of the 15 respiratory system are quantitatively adjusted to satisfy, but not exceed, an animal"s maximum 16 requirement for oxygen. We test this in the respiratory system of the adult migratory locust Locusta 17 migratoria by comparing the aerobic capacity of hopping and flight muscle with the morphology of 18 the oxygen cascade. Maximum oxygen uptake by flight muscle during tethered-flight is 967 

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... 76 19 mol h -1 g -1 (body mass-specific,  95% CI), whereas the hopping muscles consume a maximum of 20 158  8 during jumping. The 6.1-fold difference in aerobic capacity between the two muscles is 21 matched by a 6.4-fold difference in tracheole lumen volume, which is 3.5×10 8  1.2×10 8 m 3 g -1 in 22 flight muscle and 5.5×10 7  1.8×10 7 in the hopping muscles, a 6.4-fold difference in tracheole inner 23 cuticle surface area, which is 3.2×10 9  1.1×10 9 m 2 g -1 in flight muscle and 5.0×10 8  1.7×10 8 in the 24 hopping muscles, and a 6.8-fold difference in tracheole radial diffusing capacity, which is 113  47 25 mol kPa -1 h -1 g -1 in flight muscle and 16.7  6.5 in the hopping muscles. However, there is little 26 congruence between the 6.1-fold difference in aerobic capacity and the 19.8-fold difference in 27 mitochondrial volume, which is 3.2×10 10  3.9×10 9 m 3 g -1 in flight muscle and only 1.6×10 9  28 1.4×10 8 in the hopping muscles. Therefore, symmorphosis is upheld in the design of the tracheal 29 system, but not in relation to the amount of mitochondria, which might be due to other factors 30 operating on the molecular level. 31