358 FISHES CHAP. 
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 expul- 
sion of gas from the air-bladder through the ductus pneumaticus 
and mouth, and in others, as in Misgurnus fossilis, they are pro- 
duced by the rapid ejection through the anus of bubbles of air 
previously taken in at the mouth. 
(¢) Sounds produced through the agency of muscles connected 
with the air-bladder—In addition to its usual function as a 
Fic. 206.—The air-bladder and elastic-spring-mechanism in Auchenipterus nodosus. A, 
Cavity of the bladder exposed by the removal of its ventral wall: a.c, anterior 
chamber; cl, clavicle; c.tr, crescentic process of the tripus; d.c, left lateral 
chamber ; J.s, longitudinal septum separating the two lateral chambers ; oes, 
oesophagus ; p.s, pectoral spine ; ¢.s, the narrow transverse septum which partially 
separates the anterior from the two lateral chambers. B, Ventral view of the 
anterior vertebrae, to show the elastic springs: es, the oval bony plates in which the 
elastic springs terminate ; 71, first rib ; ¢.p°, transverse process of the fifth vertebra ; 
v1, first vertebral centrum ; cl, oes, and ps, asin A. (From Bridge and Haddon.) 
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. 
In the South American Siluroid, Auchenipterus nodosus, the 
transverse processes of the fourth vertebra are bent downwards 
and backwards, and at the same time become converted into 
flexible and highly elastic springs (Fig. 206, B). Their distal 
extremities expand into oval bony plates which are imbedded in 
the anterior wall of the air-bladder, and often cause the latter 
to bulge inwards (Fig. 206, A). From the occipital region of 
the skull arise two powerful muscles which pass backwards to 
