FLYING FISHES AND THEIR HABITS. 



509 



As almost every oxternal feature is characteristic, so are many 

 internal parts. In connection Avitli the longitudinal arch or convex- 

 ity of the l)ack, so different from the straightness of that of the Gur- 

 nards, a very renuiricable deviation of the air bladder fi-om normal 

 relations is noteworthy ; the dorsal curvature, indeed, is a coordinate 

 of an otherwise unexampled position of the bladder. 



The air, or swimming, bladder is unique in character, as Calder- 

 wood states, in that " it is not situated below, but | niostly J above, 

 the vertebral column, not forming part of the abdominal contents, 

 but situated dorsally in a special cavity [recess] of its own. ^A^ien 

 the abdominal cavity is opened ventrally, and the viscera removed, 

 only the ventral surface of the l)ladder is seen, forming part of the 

 dorsal boundary of the cavity. Seen from this point of view, it is 

 iormed of a broad central portion, white and tendinous, and of two 

 lateral portions strongly muscular.'' The j^hysiological significance 

 of this comes into view when 

 we consider one of the habits 

 or aptitudes of the fish. 



The structure and position 

 of the air-bladder are adapt- 

 ed for keeping the Dactylop- 

 terid Avith back upward in 

 the air in spite of the form 

 of the body and its relation 

 to the vertebral axis. " The 

 bladder, being prevented 

 from expanding when the 

 pressure from the surround- 

 ing Avater is suddenly re- 

 moved, the high dorsal position of the sccondar}^ portion Ijecomes of 

 the greatest possible advantage." It helps the fish to emerge from 

 the water and maintain its equilibrium in the air. 



Such are the most characteristic features of the Dactylopterids com- 

 mon to all the members of the family. The species are few — about 

 half a dozen — and closely related to each other, all being strictly 

 congeneric. 



It might naturally be supposed that fishes so specialized in form, 

 so peculiar in appearance, and so remarkable for the development of 

 their pectoral fins and their unusual functions, would have received 

 distinctive English names, but such is not the case. Flying gurnards 

 or flying gurnets are the general names given in most Avorks. but 

 they are mere book names and not of the common people; further, 

 the names are deceptive and haA'e often misled, for the fishes are not 

 very closely related to the true gurnards or gurnets, although more 

 so than to any other fishes. Bat-fish is a designation for the common 



Fju. •i.—Dactylui>tcrux rol/lmis: Shoulder girdle. 

 (After Boulenger.) 



