xni SOUND-PRODUCING ORGANS 357 



duced. In the Bull-head (Coitus scorpius) the preoperculum is 

 modified for stridulation, and in Dactylopterus the hyomandibular 

 bone ; in other Fishes, as in some Siluroids {e.g. species of Doras], 

 stridulation takes place between a basal process from the great 

 spine of the pectoral fin and the wall of a socket in the cleithrum 

 into which the process is received, or between the small first 

 spine of the dorsal fin and a roof-like process at the upper ex- 

 tremity of the first interspinous bone ; also, in a somewhat similar 

 fashion in the anterior dorsal fin of such widely different Fishes 

 as certain Trigger-Fishes (Sclerodermi) pertaining to the genera 

 Balistes, Monacanthus, and Triacantlius, Acanthurus chiruryus 

 (Acanthuridae), the Boar-Fish (Capros aper\ Centriscus scolopax 

 (Centriscidae), and the Three -spined Stickleback (Gastrosteus 

 aculeatus} ; and even between the spinose ray of the pelvic fin 

 and the basipterygium in Triacanthus, Oapros, and Gastrosteus. 



In the "Drumming" Trigger-Fish (Balistes aculeatus\ l 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 pro- 

 duced by the grinding of the teeth in Pigs and Euminants ; and 

 Moseley 2 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." 



(&) Breathing sounds. Characteristic breathing or murmur- 

 ing sounds, or " bruits de souffle " as Dufosse terms them, are 



1 Mobius, Sitz. d. Berlin. Akad. d. Wiss. 1889, p. 999. 

 2 Notes by a Naturalist on H.M.S. " Challenger," London, 1879, p. 51. 



