Physical Properties

Abstract

Many arthropods possess transparent regions in their cuticle and some are transparent all over. The functional interpretations are varied and interesting. In water, and especially among plankton, transparent cuticle provides good camouflage (e.g. Leptodora; larvae of Corethra). To provide for light admission, it is obvious that the cuticle over eyes and ocelli should be transparent. Furthermore, light also reaches other photosensitive regions through transparent cuticle, for example the cuticular. window over the pupal brain in Antheraea pernyi which permits photoperiodic control of diapause (Williams and Adkisson, 1964). Photosensitivity is shown by the terminal abdominal ganglion in Periplaneta (Ball, 1965) and by the epidermis in Schistocerca (Neville, 1967c), made possible in both cases by relatively transparent cuticle. Transparent cuticle is also required by light emitting insects (glow-worms and fireflies), as well as for allowing epidermal pigments to be visible through the cuticle. Furthermore, it is a requirement of multiple constructive interference systems to allow the reflection of physical colors. In spiders (Millot, 1949), reflection of light from uric acid crystals in the intestinal diverticula is made possible by overlying transparent cuticle. Transparent cuticle also makes possible the method of active color change of the grasshopper Kosciuscola tristis, in which epidermal pigment granules migrate (Key and Day, 1954).