1. Chitin purifications alter the structure of cuticular membranes of insects more or less extensively.2. Our data agree with the x-ray diffraction studies of Fraenkel and Rudall in showing:(a) The cuticle cannot be viewed as a rigid chitin framework iii the interstices of which other components are deposited.(b) Protein extraction methods have no value for localization of membrane components.(c) Purified chitinous membranes have no significance for studies on the permeability of arthropod cuticle.3. Several but not all types of membranes after purification yielded microfibers of chitin which after drying have diameters of < 100 to 300 A< 0.01 to 0.03 µ). It is suggested that these values may represent chitin micelle diameters.4. Unexpected diversity in chitin patterns was obtained. Possible interpretations are discussed, and it is suggested that chitin cross-linkages vary considerably from one type of membrane to another type.5. Chloroform and acetone remove the lipid epicuticle without affecting the str...