In recent work on the deposition of the epicuticle, Wigglesworth (1946) has shown that, in Rhodnius prolixus, not only is the epicuticle a composite structure comprising several distinct layers, but that the pore canals, which hitherto have been believed to terminate at the base of the epicuticle, do in fact penetrate its innermost regions. Wigglesworth extends the term epicuticle to cover the four outer layers of the cuticle in Rhodnius. The innermost of the four is a cuticulin layer which is followed by a polyphenol layer, a wax layer and an outer cement layer respectively. The pore canals penetrate the cuticulin layer.