water loss. The instantaneous degree to which a spiracle is open therefore reflects a tradeoff between O₂ uptake, CO₂ release, and water loss.

Morphology and valve structure

In insects, the external spiracular opening commonly leads into an atrium and a valve apparatus that regulates airflow into the tracheal trunks. The rim of the opening (often termed the peritreme), is typically a thickened, sclerotized region of cuticle that frames the aperture and serves as an attachment surface for valves.

The

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