SALMON. 165 



conveyed to a pond or pool of running 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 ; but with 

 this arises the belief that from some perhaps scarcely perceptible 

 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 first 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 difference 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 Avith 

 the peculiarities 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 known 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 bulk, in addition to the season of 

 emigration; as well as that also a retardation of growth 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 

 from an intrinsic conformation of its parts, of which the nervous 

 organization is the chief; so that, as we know the nerve of 



