xl AIR-BLADDER. 



Armado, is remarkable for a harsh grating noise which it emits when caught 

 by hook and line : this can be distinctly heard while it is still beneath the 

 water. The cuckoo-gurnard (Trigla pini) and the maigre (Scicena aquila) 

 utter sounds, not only while being removed from the water, but the latter 

 likewise, when swimming in shoals, emits, grunting or purring noises that 

 may be heard from a depth of 20 fathoms. The Corvina nigra, a fish in the 

 Tagus, emits sounds resembling the vibrations of a deep-toned bell, gong, 

 or pedal-pipe of an organ. Herrings (Clupea liarengus), when the net has 

 been drawn over them, have been observed to do the same. The fresh-water 

 bullhead (Cottns gobio) emits similar sounds. At Madras I obtained several 

 live sheat-fishes, Macrones vittatus, locally termed " fiddler fish/' and on 

 touching one which was lying on some wet grass, it erected its armed spines, 

 emitting a sound resembling the buzzing of a bee, and apparently in anger 

 or fear. Canon Tristram when in Palestine obtained some .amphibious siluroid 

 fish, Clarias macracanthus, which on being taken in the hand " squealed and 

 shrieked with a hissing sound like a cat at bay, and rapidly floundered 

 back to the streamlet, working their way- rapidly among grass and over 

 gravel." 



AIR-BLADDER. 



Prior to noticing the functions of respiration, some remarks will be 

 necessary on the air-bladders of fishes, also termed the swim-bladder, and the 

 air-sac or air-vessel (fig. 4, page xviii, vn, vn'). It is a single or variously 

 sub-divided sac; or it may be two sacs, partially or completely separated one 

 from the other. Situated above the centre of gravity,* it lies beneath the 

 vertebral column or backbone, from which it is more or less divided by the 

 kidneys, while inferiorly the peritoneum is between it and the intestines. As 

 this organ isentirely absent, or ceases to be developed in many fishes, and may 

 be present or wanting in species belonging to the same genus, it would appear 

 that it is not indispensable to the existence of these animals, its functions 

 being under certain conditions accessory or supplemental, to those of other 

 organs of the body ; while it is generally observed that the urinary bladder is 

 largest in those forms where the air-bladder is absent. In the embryo it 

 originates as a bud or offshoot from the upper portion of the alimentary 

 canal, or even from the stomach ; this offshoot next elongates into a blind 







tube, which enlarges at its terminal extremity into what will eventually form 

 the air-bladder. Consequently at some period of a fish's existence there 

 must of necessity be a tube connecting the air-bladder (should one exist) 



* Were the air-bladder below the centre of gravity, or its contents evacuated into the abdominal 

 cavity, the fish (unless its fins were very greatly developed) would roll over on its back, as we see 

 occurs in Tetrodons and Diodnns, wlien-they inflate their (esophageal sac. 



