However, the real importance of an early river has little or no connexion with the periods of the spawning process; because it is not so much the breeding fish that are of individual value in winter, as those which, having no intention or requirement to spawn until the following autumn, enter the fresh waters because they have already completed the days of their purification in the sea. Although, when viewed in the relation of time, they may seem to form the continuous succession of spawning fish which have come up _gravid_ from the ocean during the later months of autumn, they are in truth rather the _avant-couriers_ of the newer and more highly-conditioned shoals which show themselves in early spring. We believe that fresh-run fish may be found in all our larger rivers during every month throughout the year, though we cannot clear up their somewhat anomalous history, nor explain why the breeding season, as among land creatures of identical natures, should not take place more uniformly about the same time. It is by no means improbable, however, that, as grilse seek our fresh waters at different periods from adult salmon, so salmon of a certain standing may observe different periods of migration from those of dissimilar age. If, as many suppose, the earliest fish are those which have soonest spawned during the preceding autumn, and have since descended towards and recovered in the sea,--then a precocious spawning would necessarily lead to the speediest supply of clean fish in mid-winter; but the fact referred to has not been ascertained, and it may therefore still be as reasonably alleged that the winter fish (an opinion supported by the fact of their unusually large size) have continued in the sea since spring. At least a majority of them, (for they differ somewhat in their aspect and condition,) instead of having spawned soonest in autumn, have probably rather spawned last of all during the preceding spring, and so required for their recovery a corresponding retardation of their sojourn in the sea. The reasons why grilse seldom show themselves till the summer is well advanced, are very obvious, now that we have become conversant with their true history. They were only smolts in the immediately preceding spring, and are becoming grilse from week to week, and of various sizes, according to the length of their continuance in the sea. But they require at least a couple of months to intervene between their departure from the rivers in April or May, and their return thither;--which return consequently commences, though sparingly, in June, and preponderates in July and August.