ABSTRACT
The great majority of insects are air-breathing terrestrial animals. They are of small size, with a consequent large surface-to-volume ratio, and therefore an urgent need for a waterproof surface structure. The cuticle may be hard, stiff, and horny, or flexible and extensible, but its permeability to water is not necessarily related to its hardness. Some of the most pliable cuticles are the most impermeable. The epicuticle is responsible for the impermeability of the cuticle and particularly its power of preventing loss of water by transpiration. The water in the cuticle comes very close to the surface. The laminated cuticle of chitin and protein doubtless contains water throughout, and the pore canals and tubular filaments also have water in the lumen. Most cuticles become permeable to water if the surface is lightly rubbed with an abrasive dust. It is often supposed that the epidermal cells below the cuticle may actively control the water content of the cuticle.
