XIII SOUND-PRODUCING ORGANS ws 
duced. In the Bull-head (Cottus 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 Triacanthus, Acanthurus chirurgus 
(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 7’riacanthus, Capros, and Gastrosteus. 
In the “ Drumming” Trigger-Fish (Balistes aculeatus),’ 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 Ruminants; and 
Moseley” 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 murmur- 
ing sounds, or “bruits de souffle” as Dufossé 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. 
