1. The effect of temperature alone upon the permeability of arthropod cuticles has been investigated by measuring the rate of transpiration into a constant saturation deficit at a number of temperatures.

2. The permeability of the cuticles of Oniscus asellus and Lithobius sp. is little affected by temperature.

3. The cuticles of Calliphora erythrocephala, Glossina palpalis, Blatta orientalis and Periplaneta americana become progressively more permeable as the temperature is raised from 30 to 50, or 55° C. That of Tenebrio molitor larvae behaves similarly, but the increase in permeability is less marked until the temperature rises above 40° C.

4. The progressive increase in permeability of the cuticle of Periplaneta is entirely eliminated if the soft wax coating is removed.

5. The increase in permeability of the insect cuticle with temperature is approximately exponential and cannot result from a single, abrupt change in a wax layer at a ‘critical temperature’. Possible physical bases for a continuous change are discussed.

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