Relationships between uterus and eggs in cestodes from different taxa, as revealed by scanning electron microscopy

Uterine organization and interaction with developing eggs in Tetrabothrius erostris (Tetrabothriidea), Nippotaenia mogurndae (Nippotaeniidea), Arostrilepis tenuicirrosa, and Monocercus arionis (Cyclophyllidea), cestodes belonging to three different orders, were investigated by scanning electron microscopy. The interactions were traced from sexually mature to gravid proglottids for all species. Pieces of evidence of interactions among these species include specific tight contacts between microlamellae of the uterine epithelium and the egg capsule, networks of fibrils between eggs and uterus, or numerous branched diverticula of the uterine wall that surround eggs or combinations of these. The contacts between uterine epithelium and eggs take place in mature and post-mature proglottids, at a period of development when eggs are newly formed and the embryos are rapidly developing. The eggs grow and develop actively in tight contact with the uterine wall. The maximum diameter of eggs increases 1.5-2 times (or 3.5-4 times in M. arionis) during development. In all species, the intimate contacts between uterus and eggs have weakened or disappeared by the time the proglottids have become gravid. The association between uterus and eggs thus appears as strong evidence of active trophic interaction (or matrotrophy) between the parent organism and developing eggs.