After remaining a short time in this situation, and feeling about with the extremities of its wings, as if to be convinced that the business was properly executed, it dropped into the nest again. Dr. Jenner made several experiments in different nests, by repeatedly putting in an egg to the young Cuckoo, which he always found to be disposed of in the same manner. It is very remarkable that nature seems to have provided for the singular disposition of the Cuckoo in its formation at this period; for, different from other newly-hatched birds, its back, from the scapulae downward, is very broad, with a considerable depression in the middle, which seems intended for the express purpose of giving a more secure lodgment to the egg of the hedge-sparrow or its young one, while the young Cuckoo is employed in removing either of them from the nest. When it is about twelve days old, this cavity is quite filled up, the back assumes the shape of that of nestling birds in general, and at that time the disposition of turning out its companion entirely ceases. The smallness of the Cuckoo’s egg, which in general is less than that of the hedge-sparrow, is another circumstance to be attended to in this surprising transaction, and seems to account for the parent Cuckoo’s depositing it in the nest of such small birds only as these. If she were to do this in the nest of a bird that produced a larger egg, and consequently a larger nestling, the design would probably be frustrated, the young Cuckoo would be unequal to the task of becoming sole possessor of the nest, and might fall a sacrifice to the superior strength of its partners. Dr. Jenner observes, that the egg of two Cuckoos are sometimes deposited in the same nest; and gives the following instance which fell under his observation. Two Cuckoos and a hedge-sparrow were hatched in the same nest; one hedge-sparrow’s egg remained unhatched. In a few hours a contest began between the Cuckoos for possession of the nest; and this continued undetermined till the afternoon of the following day, when the one which was somewhat superior in size, turned out the other, together with the young hedge-sparrow and the unhatched egg. The contest, he adds, was very remarkable; the combatants alternately appeared to have the advantage, as each carried the other several times nearly to the top of the nest, and again sank down oppressed by the weight of its burden; till at length, after various efforts, the strongest of the two prevailed, and was afterwards brought up by the hedge-sparrow. The American Cuckoo, or Cow bird, is quite different in its habits to the European Cuckoo, as it builds a nest for its eggs, and hatches its young itself like other birds. [Illustration: THE COMMON GREEN WOODPECKER, (_Picus viridis_,)]