NATURAL HISTORY OF THE SALAfON. 71 



M very coiisj)iciious fish, may be intercepted on its way 

 fi'om the north, but it lias never yet been seen to the 

 south of the Tweed ; and if its instinct was not perfect, 

 the Dee, Don, and other rivers, by this time of day, 

 would abound with it, as the Tweed does." There are 

 here two serious errors in matter of fact, as well as a 

 correct statement which goes quite against Mr. Mac- 

 kenzie's argument. One of the errors we are not much 

 concerned to correct here : " lilack-tail" is the local name 

 not for the bull-trout {Sahno eriox), but for a very much 

 smaller fish — one of the tribe of the Sahno albus, now 

 generally held by naturalists to be only the young of the 

 Salmo trutta, or whitling. The other error, which we 

 have a greater interest in correcting, is the statement 

 that the bull-trout is " never seen to the south of the 

 Tweed," when, in fact, the two rivers immediately to the 

 south, the Aln and the Coquet, are full of that species, 

 to the almost entire exclusion of salmon and £rilse. Mr, 

 Mackenzie, however, is perfectly correct in saying, that 

 if the instinct of the Eriox, like that of migratory fish in 

 general, were not pretty nearly perfect, it would be a 

 common fish in the rivers to the north of Tweed, the 

 mouths of which it is held to pass in its marine migra- 

 tions. The facts as to the Sahno eriox, or l)ull-trout, 

 are, that in the Tweed that species is four times more 

 numerous than the adult salmon, and as numerous as 

 both salmon and grilse taken together ; that in the two 

 rivers to the south of Tweed, there are apparently about 

 fifty bull-trouts to one salmon or grilse ; but that in the 

 Forth, the Tay, and other large and accessible rivers to 

 the north, the species is filmost a stranger. In short, the 



