The 'epicuticle' in Rhodnius consists of four layers. From within outwards these are: (i) the 'cuticulin layer' composed, it is suggested, of polymerized lipoproteins tanned by quinones; (ii) the 'polyphenol layer' rich in dihydroxyphenols; (iii) the 'wax layer' responsible for the waterproofing of the cuticle; (iv) the 'cement layer' of unknown nature protecting the wax. The pore canals appear to penetrate the cuticulin layer. The oenocytes produce the lipoproteins which are deposited by the epidermal cells to form the cuticulin layer. The polyphenols then appear at the tips of the pore canals as minute droplets which unite to form a continuous film over the surface of the cuticulin. The wax is then secreted, also by the epidermal cells, and laid down over the polyphenol layer immediately before the old skin is shed. The cement is secreted by the dermal glands and poured out over the surface of the wax within an hour after moulting. The storage and use of the reserves of glycogen, fat and protein during the moulting process are described.