186 SHAW'S EXPERIMENTS. [CHAP. v. 



became sinolts ; and all who saw them on that day when they 

 were caught by Mr. Shaw were thoroughly convinced that they 

 were true salmon smolts. In March 1835 Mr. Shaw repeated 

 his experiments with twelve parrs of a larger size, taken also 

 from the river. On being transferred to the pond, these so 

 speedily acquired the scales of the smolt that Mr. Shaw 

 assumed a period of two years as being the time at which the 

 change took place from the parr to the smolt. The late Mr. 

 Young of Invershin, a well-known authority on salmon life, was 

 experimenting at the same time as Mr. Shaw, and for the same 

 purpose namely, to determine if parr were the young of the 

 salmon, and, if so, at what period they became smolts and pro- 

 ceeded to the sea. Well, Mr. Shaw said two years, and Mr. 

 Young, who was at that time manager of the Duke of Suther- 

 land's fisheries, said the change took place in twelve months ; 

 others, again, who took an interest in the controversy, said 

 that three years elapsed before the change was made. The 

 various parties interested held each their own opinion, and it 

 may even be said that the disputation still goes on ; for 

 although a numerous array of facts bearing on the migration 

 have been gathered, we are still in ignorance of any regulating 

 principle on which the migratory change is based, or to ac- 

 count for the impulse which impels a brood of fish to proceed 

 to sea divided into two moieties. Mr. Shaw watched his young 

 fry with unceasing care, and described their growth with great 

 minuteness, for a period extending over two years, when his 

 parrs became smolts. Mr. Young, in a letter from Invershin, 

 dated January 1853, says, pointedly enough " The fry re- 

 main in the river one whole year, from the time they are 

 hatched to the time they assume their silvery coat and take 

 their first departure for the sea. All the experiments we have 

 made on the ova and fry of the salmon have exactly corre- 

 sponded to the same effects, and none of them have taken 

 longer in arriving at the smolt than the first year." 



