LOPHOBRANCHII AND PLECTOGNATHI. 585 



spines which nature has bestowed upon them for their de- 

 fence ; for these spines are invested with a viscous liquor, 

 which may be poisonous, and calculated to produce inflam- 

 mation in the wounds which they cause. 



Besides their air-bladder, the balistes have also the 

 faculty of increasing their volume, and of rendering them- 

 selves much lighter in the water, by filling their bodies with 

 a great quantity of air. This must supply the weakness of 

 their fins, and contribute to their swifter motion through the 

 water. When these singular fishes are desirous of descend- 

 ing into the depths of the sea, they expel the air through the 

 aperture of their mouth and gills, by compressing themselves 

 almost suddenly ; and it is thus that they send towards the 

 surface of the water a hissing sound more or less prolonged. 

 Black, ashen, blue, yellow, and red, are the colours which 

 serve to adorn these fishes, which live in the warmest seas of 

 India and America. Two species only inhabit the Mediter- 

 ranean. 



