The structure of the spiracular gills of Eutanyderus (Tanyderidae) is described. The surface of the gill bears a plastron that opens into the spiracular atrium at the base of the gill. Blood and epidermis are present in the gill lumen in the pharate adult stage. These tissues are completely isolated from the living animal at the pupal-adult moult. Although the cuticle of the spiracular gills is relatively thick, it is not rigid and the spiracular gills are flattened even when exposed to relative humidities as high as 70 %, and it is suggested that turgidity in the living gill is achieved by the absorption of water by the isolated tissue.