194 KEY. MR. WILLIAMSON'S OPINION. [CHAP, v, 



drives them from the sea in summer impels them to the sea 

 in spring. Let the vernal direction of the propensity be 

 opposed, let a salmon be seized as it descends and confined in 

 a fresh-water pond or lake, and what is its fate ? Before pre- 

 paring to quit the river it had suffered severely in strength, 

 bulk, and general health, and, imprisoned in an atmosphere 

 which had become unwholesome, it soon begins to languish, 

 and in the course of the season expires : the experiment has 

 been tried, and the result is well known. This being an 

 ascertained and unquestionable fact, is it a violent or unfair 

 inference that a similar result obtains in the case of those 

 salmon that are forced back, from whatever cause, to the sea, 

 that the salt-water element is as fatal to the pregnant fish of 

 autumn as the fresh-water element is to the spent fish in 

 spring ? ... If there is any truth in these conjectures, 

 they suggest the most powerful reasons for resisting or removing 

 obstructions in the estuary of a river." The riddle of this double 

 migration of the salmon is likely still to puzzle us. It is said 

 that the impelling force of the migratory instinct is, that the 

 fish is preyed upon in the salt water by a species of crustaceous 

 insect, which forces it to seek the fresh waters of its native 

 river; again, that while the fresh water destroys these sea-lice 

 a new kind infests it in the river, thus necessitating a return 

 to the sea. My own experience leads me to believe that 

 salmon can exist perfectly well in the fresh water for months 

 at a time, suffering but little deterioration in weight, but 

 never, so far as I could ascertain, growing while in the fresh 

 streams, although it is certain they feed. It is a well-known 

 fact that the parr cannot live in salt water. I have both tried 

 the experiment myself and seen it tried by others ; the parr 

 invariably die when placed in contact with the sea-water. 



Mr. William Brown, in his painstaking account of The 

 Natural History of the Salmon, also bears his testimony on 

 this part of the salmon question : " Until the parr takes on 



