My Dear sir, In a letter with which you have favoured me, that of the 28th of January, you did me the honour to ask my aid in an inquiry in which you take an interest, in common, as you remark, with most naturalists, viz. the geographical distribution of species, especially that of fish. At the same time you expressed your opinion that some useful information might be procured by experiments on the impregnated ova of the latter, were they so conducted as to show what the ova are capable of bearing without loss of vitality, and under exposure to circumstances such as might be compatible with their being conveyed from one river or lake to another, adhering, for instance, to the plumage, beak or legs of birds. In reply, I acquainted you of my willingness, should I have an opportunity, to accede to your wishes; and, that occurring, having been so fortunate as to procure the means of making some experiments likely to be elucidatory, I have now the pleasure of communicating the results obtained. All the experiments I have to describe have been made on the ova of the Salmon, for which I have been indebted to two gentlemen, John Barker, Esq., of Broughton Lodge in Cartmel, and William Ayrton, Esq., of Chester. By the first, through one of his keepers, I was supplied with a considerable quantity of ova, taken from a breeding-bed in the Leven, a river that flows out of Windermere, and from a part of it near Newby Bridge, about eighteen miles distant from my house. Through the latter I obtained ova from Overton on the Dee, taken from boxes in which they had been placed in the process, as it has been called, of artificial breeding.