MALACOPTERYGII ABDOMINALES. 471 



proceed slowly, and sport along the wave, if the temperatnre 

 of the air be mild, and the radiance of the sun moderate ; 

 but when the tempest threatens, or when the sun darts his 

 ardent rays through the burning air, they sink to the 

 bottom. 



Violently loud noises, such as the sound of bells, or the 

 discharge of cannon, bodies which float upon the water, par- 

 ticularly if their colours be bright, and their surface shining, 

 terrify these bands, frequently turn them from their direction, 

 and force them to suspend their course or to return to the 

 sea. 



They also avoid rivers, the shores of whose mouth are 

 furnished with buildings, and seek those where the banks are 

 shaded with trees. 



When a dam, or a cascade, opposes itself to the progress 

 of the salmons, these fishes make the most strenuous efforts 

 to shoot beyond it. Even elevated cataracts are no insur- 

 mountable obstacle to them, and they find, in crossing them, 

 an efficacious help in the vigorous muscles which form the 

 mass of their powerful tail. With one of their sides resting 

 upon some large stones, they approximate the extremity of 

 the tail to the mouth, catch it with their teeth, and thus form 

 an arch which constitutes a powerfully tense spring ; this they 

 let go with an inconceivable rapidity, strike the water with 

 violence, and spring as Twiss has observed at Ballyshannon, 

 in Ireland to a height of twelve or fifteen feet in the air, 

 and then fall beyond the obstacle which had arrested their 

 progress. 



If any danger appears to threaten them, if they wish to 

 avoid any snare, the rapidity of* their swimming is so great 

 that the eye can scarcely follow them. Experience has 

 proved that in tranquil lakes, they can go eight or ten 

 leagues in an hour, and about twenty-four feet in a second. 



