NATURAL HISTORY OJ^^ THE SALMON. 53 



fish emigrate after the end of the first, the other half 

 after the end of the second year ; the date of departure 

 varies to the extent of weeks in different years according 

 to the temperature ; and, cceteris paribus, the two-year- 

 olds go off a week or two earlier in spring than the one- 

 year-olds. 



Although, on the whole, the evidence must, we think, 

 be held as thus establishing that one-half of the young fish 

 descend at one year, and the other half at two years of 

 age, still if this compromise is not accepted, and a de- 

 cision one way or the other is insisted upon, then it must 

 be held that by far the weightiest and best tested evi- 

 dence is in favour of two years. For, while there are 

 doubts and disputes (at least as to the first experiment) 

 in what degree the fish that left the first year exhibited 

 the migratory instinct, there is no doubt whatever that 

 a full half of the fish did not then exhibit any symptom 

 of migrativeness, but declined all invitations to remove 

 until the second year. 



The third question, AVhether the young of the salmon, 

 after descending as a smolt, ascends that same season or 

 the next, has been rather raised than laid by some rather 

 loose experiments, which is the more to be regretted, as 

 its settlement would also have conduced very greatly to 

 the settlement of the preceding point, as to the age at 

 which the smolt descends. If, at the experiment first 

 made, a portion of the Stormontfield smolts, supposed 

 to have descended to the sea at one year old, had been 

 sufficiently marked, and some of them been captured 

 that same season after their return from the sea, it 

 would have been made certain, both that the one-year- 



