The exoskeleton and musculature of the middle and posterior abdomen in female Calopteryx virgo are described (segmentsIVff), including parts of the midabdominal nervous system. Based on a sample of 16 species of Odonata with a plesiomor-phic morphology of the ovipositor (various Zygoptera, Epiophlebia, and Aeshnidae) the range of variation in the abdominalexoskeleton is documented, and a preliminary list and table of 79 characters are assembled. Abdominal muscles in Odonataare surveyed based on data from the literature. Topographic homologies between Odonata and other Insecta are discussed,with a focus on the female genitalic region and the terminal abdomen, and with consideration of previous ontogenetic stud-ies. The results are used for including outgroup scorings into the character list for Odonata. Odonata conform with manyNeoptera (e.g., Notoptera, pygidicranid Dermaptera) in the location of the female genital opening between or behind the gonapophyses VIII bases, contrasting with the VIIth-segmental openings in other Neoptera (e.g., Dictyoptera, Ensifera, ‘advanced’ Dermaptera), Archaeognatha, and Zygentoma. The gonangulum in most Odonata consists, like in Archaeognatha and some Dermaptera, of two separate sclerites; this contrasts with the one-piece condition of the gonangulum in other Dicondylia and Epiophlebia. The interpretation of terminal appendages in Odonata as the true cerci is supported by musculature data, and it is shown that previous counter-arguments are invalid. While Epiophlebia is in many characters highly peculiar among Odonata, the abdominal characters provide no resolution for the relationships between Epiophlebia, Zygoptera, and Anisoptera. The monophyly of Zygoptera receives considerable support.