The dome-shaped ('campaniform') cuticular structures found in small depressions on the lateral antennular flagella of the lobster (Homarus gammarus) were investigated by means of electron-microscopic methods. Each dome (diameter: 4-5 micron), which is surrounded by a 3-5 micron wide cuticular collar, is associated with a cell (soma size: long axis 90 micron, short axis 24 micron) showing fine-structural details characteristic of a dermal gland, e.g., a ductule lined by thin (cuticulin-like) cuticle and a well-developed granular endoplasmic reticulum. This ductule ends within the dome, which consists of spongious cuticle and, when seen from outside, resembles the cuticular cap of a typical campaniform sensillum of insects (Fig. 1 b). The fine-structural findings, especially the lack of any sensory element, are clear evidence against previous descriptions of these structures as representing 'campaniform sensilla of crustaceans'.