SALMON. 
165 
conveyed to a pond or pool of nrnning water, where the fol- 
lowing stages of development and growth might be traced from 
day to day. Our knowledge of some of the habits and changes 
of the young of the Salmon has been thus extended; hut with 
this arises the belief that from some perhaps scarcely percejitible 
influences arising from the small degree of deviation to which 
they have been subjected in their removal from the natural 
action of the river, as regards its depth, the nature of the soil, 
and other causes, including an unnatural manner of impregnation; 
the regular course of development has been interfered with; and 
as experience proves that the Salmon, perhaps more than any 
other fish, is thus liable to be influenced, it may in this manner 
be explained why it is that a portion of these young fishes should 
be ready to pass out of the fresh water early in the fii’st year 
of their existence, while others of them, and it -would appear, 
almost if not altogether exclusively, the males are not ready for 
this emigration before the second, or even the third year of 
their age. 
As bearing on the same subject, it seems highly probable 
also that much difterence will be found to exist between rivers 
not far distant from each other; and which from the variation 
of times in which they are visited by the fish are termed early 
or late; a knowledge of the causes of which is yet obscure, 
and to study them fully would demand an acquaintance with 
the 23eculiarities of every river in the kingdom. We shall have 
occasion to shew that in the rivers of the south and west of 
England no such delay is kno-nm in the departure of the young, 
as is reported in the north ; and as it is also certain that some 
causes have operated to produce in different rivers considerable 
variation of shape and hulk, in addition to the season of 
emigration; as well as that also a retardation of groAvth has 
been effected to and beyond the third year by artificial means, 
the conclusion seems unavoidable, that there is some special 
circumstances which produce these variations, and that they may 
be obviated when the subject is better understood. 
But there is a limit to every degree of variation in a living 
animal; and amidst the large amount of its changes there exists 
a sub-stratum of regularity of habit and action, which is derived 
fiom an intrinsic conformation of its parts, of which the nervous 
organization is the chief; so that, as we know the nerve of 
