4 796 Fishes. 



seldom seen by the angler, and after which it ceases to be found in 

 fresh-water rivers. Secondly, proof that the fish we call salmon fry 

 (smolts), taken in salmon rivers by anglers during the months of April 

 and May, do really proceed to the ocean, and return after a period to 

 the rivers as grilse, salmon trout, and salmon. The facts ascertained 

 by Dr. Knox, in conjunction with the previous observations of others 

 who have attended to the subject, go towards the answer of the first 

 question, whilst the experiments made in Sutherlandshire, on the Lax- 

 ford and Divard may be considered as a reply to the second. Fry 

 marked in April returned as grilse on the 25th June." 



Soon after these observations had been made and submitted to the 

 Royal Society of Edinburgh, others entered on the field, and the 

 Duke of Buccleugh must have taken some interest in the matter, since 

 he permitted one of his game-keepers, a Mr. Shaw, to experiment on 

 the ova of the salmon, and on what he called the parr. The ideas 

 of this person respecting the parr have no foundation whatever either 

 in observation or experiment ; the experiments he made led to what 

 is called the two-years' theory of the May smolt. By confining the 

 young of the salmon in ponds and boxes, and placing them under 

 artificial circumstances, he contrived to retard the growth of the fry to 

 the extent specified : thus he first misled himself, and then others. 



When I first heard of the two years' theory of the age of the May 

 smolt, my remark was this — "Wait a little, and another experi- 

 menter, proceeding on the same principles or want of principle, will 

 prove to you that three years is the age ; and after a little while 

 another of the same class will show you that one year is the true 

 period." The prediction was verified to the letter. Mr. Hannay, of 

 Kircudbright,* showed by experiment that the smolt is a three years' 

 old fish ; Mr. Young, of Invershin, by the same method, proves 

 one year to be the true age, and the experiment repeated at this 

 moment by my esteemed friend Dr. Esdaile, of Perth, on ova reared in 

 ponds adjoining the Tay, has brought to a sudden close, and for ever, 

 the two-year' old theory, a delusion of the plainest character, but yet 

 sufficient to mislead many naturalists. Scientific continental natural- 

 ists, finding persons engaging in these controversies who are not 

 scientific men in any sense of the term, stand aloof. 



Whilst I now write my friend Dr. Esdaile, to whom the public is 

 already deeply indebted for services rendered humanity in India, 

 and who I am proud to say was at one time my student, informs 



* See this gentleman's letter, published by me in the work already quoted ; the 

 original is now before me. 



