Histological and histochemical studies on the cuticle of A. immaculifrons from the third larval instar to the imago revealed 3 types of cuticular organisation. The first type was present in larval instar 3 to 9; instars 10 to 13 had type-II, while the imago had type-HI. The type-I cuticle had 3 layers, i.e. epi-, exo- and endocuticle. The protein of the epicuticle as well as that of the exocuticle is stabilized by disulphide linkages. The type-II epicuticle resembled its counterpart in type-1 in the mode of hardening but the exocuticle had undergone hardening involving both aromatic substances and organic sulphur (R-S-R). Lying between the exocuticle and the endocuticle was a new layer, the mesocuticle. This new layer had undergone primary tanning. The type-111 cuticle differed from the first two, both in its histology and histochemistry. The epicuticle was bilaminar, having an outer lipid layer and an inner lipoprotein lamina. The inner epicuticle as well as exocuticle had undergone hardening by aromatic tanning. However, the mesocuticle resembled its homologue in the preceding stage in chemical composition. The protein from the 3 types of cuticle was extracted and analysed by electrophoretic and chromatographic methods. These results substantiated those obtained by histochemical procedures. Changes in the proportion of the exoskeleton to body weight in larvae and adults were also recorded. The results are discussed in relation to the evolution of aerial life.