358 



FISHES 



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 

 taenid), and the European Siluroid, Silurus glanis. According 

 to Dufosse 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. 



(c) Sounds produced through the agency of muscles connected 

 with the air-bladder. In addition to its usual function as a 



p.s. 



FIG. 206. The air-bladder and elastic-spring-mechanism in A^lchen^pterus 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 ; l.c, left lateral 

 chamber ; l.s, longitudinal septum separating the two lateral chambers ; oes, 

 oesophagus ; p.s, pectoral spine ; t.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 ; r 1 , first rib ; t.p 5 , transverse process of the fifth vertebra ; 

 r a , first vertebral centrum ; cl, oes, andps, as in 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 



