MIGRATIONS. 119 



each pair being at the distance of, from three 

 to six feet from the preceding one ; next come 

 the old, and after them the young males in the 

 same order. 



The noise they make in their transit, heard 

 from a distance, sounds like a far off storm. In 

 the heat of the sun and in tempests, they keep 

 near the bottom; at other times they swim a 

 little below the surface. In fair weather they 

 move slowly, sporting as they go at the surface, 

 and wandering again and again from their direct 

 route ; but when alarmed they dart forward with 

 such rapidity that the eye can scarcely follow 

 them. They employ only three months in 

 ascending to the sources of the Maragnon, the 

 current of which is remarkably rapid, which is 

 at the rate of nearly forty miles a day ; in a 

 smooth stream or lake, their progress would 

 increase in a fourfold ratio. Their tail is a very 

 powerful organ, and its muscles have wonderful 

 energy ; by placing it in their mouth they make 

 of it a very elastic spring, for letting it go with 

 violence they raise themselves in the air to the 

 height of, from twelve to fifteen feet, and so 

 clear the cataract that impedes their course ; if 

 they fail in their first attempt, they continue 

 their efforts till they have accomplished it. The 

 female is stated to hollow out a long and deep 

 excavation in the gravelly bed of the river to 



