ORN.—I cannot agree with you: the legs of the fœtus are folded up in the womb of the mare; and neither the colt nor the chicken can ever have performed, in the embryo state, any motions of their legs similar to those which they have perfectly at their command when born. Young birds cannot fly as soon as they are hatched, because they have no wing feathers; but as soon as these are developed, and even before they are perfectly strong, they use their wings, fly, and quit their nests without any education from their parents. Compare a young quail, when a few days old, with a child of as many months: he flies, runs, seeks his food, avoids danger, and obeys the call of his mother; whilst a child is perfectly helpless, and can perform few voluntary motions: has barely learnt to grasp, and can neither stand nor walk. But to see the most perfect instance of instinct, as contrasted with acquired knowledge, look at common domestic poultry, as soon as they are excluded from the egg: they run round their mother, nestle in her feathers, and obey her call, without education: she leads them to some spot where there is soft earth or dung, and instantly begins scratching with her feet; the chickens watch her motions with the utmost attention; if an earthworm or larva is turned up, they instantly seize and devour it, but they avoid eating sticks, grass, or straws; and though the hen shows them the example of picking up grain, they do not imitate her in this respect, but for some days prefer ants, or the larvæ of ants, to a barley corn. They may have heard the cluck of their mother in the egg, and having felt the warmth of her feathers agreeable, you may consider, Physicus, their collecting under her wings, and obeying her call, as an acquired habit. But I will mention another circumstance where habit or education is entirely out of the question. Does the mother see the shadow of a kite on the ground, or hear his scream in the air, she instantly utters a shrill suppressed cry; the chickens, though born that day, and searching round her with glee and animation for the food which her feet were providing for them, instantly appear as if thunder struck; those close to her crouch down and hide themselves in the straw; those further off, without moving from the place, remain prostrate; the hen looks upward with a watchful eye; nor do they resume their feeding till they have been called again by the cluck of their mother, and warned that the danger is over. PHYS.—I certainly cannot explain the acquaintance of the little animals with the note of alarm of the mother, except upon the principle you have adopted; and I fairly own, that their selection of animal food appears likewise instinctive: yet it is possible, that this selection may depend upon some analogy between the smell of these animal matters and the yolk, which was for a long time their food in the egg.