The ventral adhesive discs of the cyclopterid Eumicrotremus orbis and the gobiesocid Gobiesox maeandricus were compared in regards to structure and efficiency. The disc of E. orbis was found to be the more efficient, being able to support, on the average, 843.6 grams per square centimeter of disc area as compared to 453.8 g/cm² for G. maeandricus. The firmer, more compact nature and the greater use of the muscles in the function of the cyclopterid disc accounted for this greater efficiency. The creation of a negative pressure during the adhering process in both species was empirically demonstrated for the first time. G. maeandricus was shown to create a greater suction than E. orbis while supporting an equivalent weight. The pectoral fins were found to be vital in the function of the disc of G. maeandricus. It was concluded that the efficiency of the discs is related to body form; thus E. orbis with a globular, unstreamlined body, has the more efficient disc, while in G. maeandricus, in which the body is flattened and streamlined, the disc is less efficient. A new mechanism, described as a sliding and bending property of the lepidotrichs of the fin-rays, is presented; the role of this mechanism in the function of the adhesive disc of G. maeandricus and in the locomotive function of fins in general is discussed. / Science, Faculty of / Zoology, Department of / Graduate