Ultrastructure of the neck membrane in dragonflies (Insecta, Odonata)

This study describes and quantifies the microsculpture and ultrastructural design of the neck membrane of adult Odonata using scanning and transmissio n electron microscopy. The membranous cuticle has a complex pattern of micr ofolds, which appear to have a specialized mechanical function. The membran e has two layers of cuticle: the epicuticle and exocuticle. The outermost l ayer is the electron-opaque epicuticle, which repeats the shapes of the mic rofolds. The epicuticle has no fibrillar elements. The exocuticle is electr on-lucent and rather thin (0.5-1.5 mu m) compared with the sclerite cuticle . The cuticle microfibrils in successive lamellae are at angles to each oth er. The epidermal cells underlying the membrane have an electron-lucent mat rix filled with electron-opaque spherical vesicles of 0.1-0.4 mu m in diame ter. The behaviour of the membrane folds under loading was studied by shock -freezing experiments; these showed that the shape of the folds changed in response to head movements, and stretched under loading. A comparison of th e surface patterns of the membrane in 10 odonate species from seven familie s (Zygoptera: Coenagrionidae, Lestidae, Megapodagrionidae; Anisoptera: Cord ulegastridae, Aeshnidae, Corduliidae, Libellulidae) had not revealed any co rrelation of the measured parameters with the size, sex or systematic posit ion of species studied.