Studies of the Development of the Imaginal Cuticle of Calliphora erythrocephala

The development of the imaginal cuticle has been studied with particular emphasis on the microtrichia and the pupal moulting fluid. The microtrichia are formed from acidophil filaments of epidermal cytoplasm which remain as the cuticular pore canals after secretion of the endocuticle. Microtrichia at the base of the bristles are associated with nerves. The cuticle before emergence consists of a single-layered epicuticle less than 1 ft thick and an endocuticle 3-5 /J, thick. The epicuticle and the endocuticle of the sclerites are completely sclerotized after emergence. The pupal moulting fluid was found to be a clear, salt-free, watery liquid containing protein and lipoid and devoid of proteinases or chitinases. No evidence of dissolution was found in the pupal cuticle. The aqueous part of the moulting fluid is absorbed before emergence and this may be prevented by the addition of salts. Evidence is presented for the formation of a denatured, hydrophobic, proteinlipoid film from the moulting fluid on the surface of the epicuticle after emergence. Resistance to water loss develops after emergence and is not entirely dependent on cuticle darkening and hardening. A film of moulting fluid spread and dried on natural and artificial membranes lowers the rate of water permeation. Such films possibly are operative in regulation of water loss from the imaginal cuticle immediately after emergence. Waxy materials appear on the cuticle surface during the hardening phase. Their possible origin is discussed.