The carp Cyprinus carpio has a two-chambered swimbladder and excellent hearing. I explored the hypothesis that the anterior chamber, which connects to Weberian ossicles, is adapted for hearing by testing both chambers for material properties. I also determined displacement and auditory responses to mechanical strikes. Wall stress is higher in the posterior, strain in the anterior and modulus lower in the anterior chamber. Strikes increase pressure followed by a variable rebound that rapidly decays. Displacement and sound amplitude increase with hammer force, and amplitude is similar in both chambers for within chamber strikes but lower across chambers. Normalized for equivalent displacement, the anterior chamber produces a more intense sound. Stiffness and damping are greater for the anterior chamber, but sound spectra are similar. More intense sound production per unit of movement, greater damping and higher stiffness for the anterior chamber should all contribute to high-frequency auditory sensitivity.

In Labeo umbratus only the first three anterior vertebrae undergo any modification. These vertebrae are not completely anchylosed with each other and are closely associated with the four Weberian ossicles. Movement is however restricted between these vertebrae since this is essential for the efficient functioning of the Weberian ossicles. The first vertebra is well developed the absence of a spinous process and neural arch in the first vertebra may perhaps be explained by the findings of some workers who derive the claustrum from the former and the scaphium from the latter. A small muscle has its origin on the claustrum and its insertion in the angle formed by the dorsal and medial processes of the scaphium. A second muscle originates in the pit-like excavation of the first vertebra and is inserted on the ventral process of the scaphium. The intercalarium possesses horizontal, articular and ascending processes; a portion of the horizontal process being imbedded in the interossicular ligament. In Labeo umbratus it is unlikely that the intercalarium represents (if it does so at all) the entire neural arch of the second vertebra. From a morphological point of view it seems likely that the intercalarium may function as a lever. A transversely situated ductus endolymphaticus joins the two sacculi to each other. The sagitta, in the region of the ductus endolymphaticus has a long, lateral "wing-like" process which projects into the cavity of the sacculus. The sacculus anilagena are innervated by the n. saccularis and the n. lagenaris respectively. The ductus endolymphaticus is prolonged posteriorly into a median unpaired sinus endolymphaticus. Although the only serious objection to Weber's theory is the fact that there could be no differential action of the two ears, the basic idea seems valid. Sagemehl's theory cannot be accepted. It seems likely that the Weberian ossicles are necessary structures for audition and to the hydrostatia function of the air-bladder.