SALMONID.E. 81 



majority of instances ; but it would appear from the observations of 

 Dr. Heysham and Sir William Jardine, that if they have roved to a 

 very great distance from the estuary of their own stream, they betake 

 themselves to the mouth of the first river they reach, if its temperature 

 and the condition of its waters suits them. 



Many Tweed Salmon are occasionally taken in the frith of Forth, 

 and it is even said that in seasons when the Forth fisheries are unusu- 

 ally successful, those of the Tweed are as much the reverse. Sir Hum- 

 phrey Davy is of opinion that the taste of the waters of different 

 rivers, according as they are impregnated with different substances, 

 and the effect produced by them on the bronchiae of the fish in the act 

 of breathing, are the guides by which Salmon are led back to the streams 

 to which they have been accustomed ; and he accounts for their being 

 occasionally mistaken, by the fact that such mistakes frequently occur 

 during great floods, connected with storms, or violent motion in the 

 waters near the shore ; by which the components of the waters are 

 disturbed, and their flavor consequently altered. In confirmation of 

 this view, he relates that he " remembers in this way, owing to a tre- 

 mendous flood, catching with the fly a large Salmon which had mista- 

 ken his stream, having come into the Bush, near the Giant's Cause- 

 way, instead of the Bann. No fish can be more distinct," he proceeds, 

 " in the same species, than the fish of these two rivers, their length to 

 their girth being in a ratio of 20 : 9 and 20 : 13." 



I am not, however, inclined to adopt this explanation. For it seems 

 to me that in migratory animals of all kinds, and indeed, in some 

 instances, in domestic animals likewise, that there is some sort of sixth 

 sense, or at least some entirely distinct power, not acquired by means 

 of any of the senses of which we are cognizant, nor acting like reason, 

 by means of deduction, which enables them to, steer their course 

 through countless leagues of air or water, or over miles of uncultivated 

 land, to the places where they were bred, or to which their instincts 

 compel them to resort for the purpose of wintering, obtaining food, or 

 the like. 



And I no more believe that Salmon are guided back to their native 

 rivers by the flavor of the waters, than I do that the swallow, finds 

 his way from Africa to Europe, or from Southern to Northern 

 America, by the scent of the tainted atmosphere. 



