HAL.—Physicus has mistaken me; and I will explain. What I mentioned of the varieties of dogs as sprung from one type, he will, I am sure, allow me to apply, with some modifications, to all our cultivated breeds of animals, whether horses, oxen, sheep, hogs, geese, ducks, turkies, or pigeons; and he will allow, that certain characters gained by accidents, either from peculiar food, air, water, or domestic treatment, are transmitted to, and often strengthened in the next generation; the qualities being, as it were, doubled when belonging to both parents, and retained in spite of counteracting causes. It will be sufficient for me to mention only a few cases. The blood-horse of Arabia, is become the favourite of the north of Europe, and the colts possess all the superior qualities of their parents, even in the polar circle. The offspring of the Merino sheep retain the fineness of their wool in England and Saxony. Poultry, bantams, tumbling and carrier pigeons, geese, ducks, turkies, &c., all afford instances of the same kind; and in the goose and duck, not only is the colour of the feathers changed, but the form of the muscles of the legs and wings; those of the wings, being little employed, become weak and slender; those of the legs, on the contrary, being much used, are strong and fleshy; and it is well to know this, as, in the young birds, the muscles of the legs and thighs are the best parts for the epicure, a large quantity of flesh being developed there, but not yet hardened or rendered tough by exercise. These facts are of the same kind and depend on the same principles, as the peculiarity of the breeds or races in trouts. Fish in a clear cool river, that feed much on larvæ, and that swallow their hard cases, become yellower, and the red spots increase so as to outnumber the black ones; and these qualities become fixed in the young fishes, and establish a particular variety. If trout from a lake, or another river of a different variety, were introduced into this river, they would not at once change their characters; but the change would take place gradually. Thus I have known trout from a lake in Scotland, remarkable for their deep red flesh, introduced into another lake, where the trout had only white flesh, and they retained the peculiar redness of their flesh for many years. At first they all associated together in spawning in the brook which fed the lake, but those newly introduced were easily known from their darker backs and brighter sides. By degrees, however, from the influence of food and other causes, they became changed; the young trout of the introduced variety had flesh less red than their parents; and in about twenty years the variety was entirely lost, and all the fish were in their original white state. A very speculative reasoner might certainly defend the hypothesis, of the change of _species_ in a long course of ages, from the establishment of particular characters as hereditary. It