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Fig. 3. Phylogeny of insects (redrawn from
Gullan and Cranston, 2005)
indicating the gas exchange patterns that are shown by species within each of
the orders. Symbols for the gas exchange patterns are as follows: squares,
continuous gas exchange; circles, cyclic gas exchange; triangles,
discontinuous gas exchange. The parsimony analysis is also indicated on the
phylogeny and shows that the cyclic pattern is the ancestral condition at
rest. Discontinuous gas exchange cycles (DGCs) have been observed in only 5 of
the 30 orders of insects, while continuous and cyclic patterns have been
observed in all of the orders examined.
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