In the "Drumming" Trigger-Fish (_Balistes aculeatus_),[419] which frequents the coral-reefs off the Island of Mauritius, stridulation takes place between the postclavicles and a longitudinally grooved area on the inner surface of each cleithrum. Both the cleithra and postclavicles are in intimate relation with the air-bladder, and the sound produced by friction is apparently strengthened by the transference of the vibrations to the walls and gaseous contents of that organ. The passage of the sound-vibrations to the surrounding medium is facilitated by the fact that for a portion of their extent the lateral walls of the air-bladder are in contact with the superficial skin, which visibly shares in the vibratory movement of the bladder when the characteristic drumming sounds of _Balistes_ are being emitted. Stridulating sounds may also be produced by the friction of the upper and lower pharyngeal teeth, as in a species of Mackerel (_Scomber brachyurus_). By the grating of its teeth the Sun-Fish (_Orthagoriscus mola_) is said to emit sounds similar to those produced by the grinding of the teeth in Pigs and Ruminants; and Moseley[420] has remarked of a species of _Balistes_ that the "living Fish when held in the hand makes a curious metallic clicking noise by grating its teeth." (_b_) _Breathing sounds_.—Characteristic breathing or murmuring sounds, or "bruits de souffle" as Dufossé terms them, are {358}produced by a few Teleosts, among which may be mentioned the Eels, certain Cyprinidae, as, for example, the Carp (_Cyprinus carpio_), several species of Loaches (e.g. _Misgurnus fossilis_ and _Cobitis taenia_), and the European Siluroid, _Silurus glanis_. According to Dufossé these sounds originate in some cases from the expulsion of gas from the air-bladder through the ductus pneumaticus and mouth, and in others, as in _Misgurnus fossilis_, they are produced by the rapid ejection through the anus of bubbles of air previously taken in at the mouth. (_c_) _Sounds produced through the agency of muscles connected with the air-bladder_.—In addition to its usual function as a hydrostatic organ or "float" the air-bladder is often modified in various ways in different Teleosts, and adapted for use as a sound-producing organ.