The cuticle of the cockroach Periplaneta americana . IV. The hardening of the cuticle: phenolic tanning

During the later stages of hardening the epicuticle and the outer zone of the pre-exuvial endocuticle of Periplaneta become amber-coloured and refractory to staining. These changes are due to the inward spread of phenolic tanning which begins in the epicuticle. The epicuticle carries a polyphenol oxidase, the polyphenol responsible for tanning is derived from the blood, and there is no reason to doubt that the tanning of the cuticle of the exopterygote insect takes place in essentially the same manner as in the specialized blowfly puparium.