We investigated the gross anatomy, histology and ultrastructure of Duvernoy's glands and scanning electron microscopy of maxillary teeth of Helicops modestus, as well as its prey-handling behavior in laboratory. We later compared this histology with other species of Hydropsini. Duvernoy's glands are located in the post-ocular region, immediately behind the supralabial gland. Each gland is connected to a pair of ungrooved rear fangs by a vestibule from which the secretion is drained. Histological analysis showed that the gland is wrapped by a layer of connective tissue and consists of a glandular body formed by prismatic cells organized in acini and a duct lined with columnar cells. The prismatic cells are positive to PAS and bromophenol blue, indicating glycoprotein content, whereas the columnar ductal cells are positive to PAS and alcian blue pH 2.5, indicating the presence of acid mucous. Transmission electron microscopy showed electron-dense, heterogeneous granules in the prismatic cells, whereas the granules of the columnar cells were electron-luscent and homogeneous. The Duvernoy's glands of H. modestus are more similar to those of H. angulatus than any other species analyzed. Observations of prey-handling behavior showed that H. modestus strikes and holds fish in its mouth while repeatedly carrying out bilateral raking motions with both maxillae. Ingestion starts headfirst. We observed only a single episode of constriction. Snakes usually swallowed fish alive but clearly immobilized, suggesting that the primary function of the Duvernoy's secretion is associated with the quiescence/immobilization of the fish prey.
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