Various thin insect cuticles (tracheae, gut linings, wings, etc.) were treated with reagents known to remove or alter one or more components of these membranes. Reagents used included alkali, acid, oxidizing agents, pepsin, detergents, salt solutions and distilled water. It was found that chitin purifications lead to more or less extensive alteration of the membranes. The data agree with the x-ray analyses of Fraenkel and Rudall in showing that the chitin micelles cannot be regarded as a rigid framework in the interstices of which the other components are simply deposited; that extraction methods have no value for localization of components in cuticle, and that such purified membranes have no value for permeability work (and previous papers using such should be discredited). Several of the types of membranes yielded microfibers, in some oriented, in some random, which after drying have diameters of < 100-300 A. It is suggested that these diameters represent micelle dimensions. Unexpected diversity of chitin patterns was obtained; in the discussion it was suggested that the most reasonable explanation of this diversity is to assume that cross-linkages between chitin chains vary considerably from one type of membrane to another. It was further found that lipid solvents remove only the lipid layer while detergents remove this and also disrupt the underlying protein layers. Intensive studies on the effects of prolonged treatment with salt solutions and with distilled water suggest that isolated cuticles can be used in permeability studies only at relatively low temps. (25 C) and only when some form of parallel tests are run to show that the membranes remain reasonably near their original structure and composition.