1. The cuticle of the walking legs of adult spiders (Cupiennius saleiKeys.) was examined by both the light- and electron microscope. 2. The following layers can be distinguished from the surface inward: epi-, exo-, meso-, endo-, and subcuticle. Although various stains used in light microscopy show the meso- and endocuticle are not identical, the electron microscope reveals no clear difference between them. 3. The epicuticle is less than 0,5 μ thick and with a wavy surface resulting from riblike elevations (height and width about 1500 Å). The sequence of the 5 layers composing the epicuticle as they appear under the electron microscope suggests that these are homologous to the layers found in insects. It is therefore proposed to call them dense layer (1), cuticulin layer (2), oriented lipid layer (3, 4), and cement layer (5) respectively. 4. Microfibers can be seen in the meso- and endocuticle as well as in the exocuticle. Whereas curved patterns appear on sections parallel to the longitudinal axis of the leg, only horizontal bands of alternating degrees of electron density can be observed on cross sections. 5. The cuticular components of the various sensilla located in the cuticle of the spider leg are mainly made up of exocuticle; their characteristics are illustrated. 6. Sections reveal pore canals which extend outwards through all levels of the cuticle. Within the dense layer of the epicuticle they branch into about 10 canals of greatly reduced diameter. These almost always terminate between a pair of epicuticular ribs, and some appear to remain open after penetrating the oriented lipid layer. There is evidence that the course of the pore canals is not straight but curved, forming arches between two neighbouring laminae. 7. According to the results so far obtained from the legs there are no basic differences between the cuticle of a spider and an insect. © 1969 Springer-Verlag.
