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306 principle, and the exercise of ordinary intelligence, the last stage of lining the cup with grass may finally cease. It has ceased with the thrush, but, with the thrush, there has been a still further process of change, for it no longer plasters its nest with mud, but with decaying wood and with cow-dung. Assuming the ancestors of the bird to have once used mud, and lined the interior, as does the blackbird, there does not seem to me to be any great difficulty in explaining this change. The blackbirds that I watched building their nest, always, when the proper period arrived, flew to a certain part of a little muddy dyke (it is in a land of dykes that I reside) some little way from the plantation in which the nest was situated, and there, lying flat behind tufts and tussocks of reeds and grass, I watched them take their mud as I have described—the female, that is to say, but a husband much interested in seeing a baby carried would deserve half the credit of carrying it. Now, much nearer, probably, than this specially-resorted-to dyke was some decayed tree or tree-trunk, whilst over the fields which it intersected and which adjoined the plantation, cows or oxen sometimes grazed. Here, again, a change in the working material might prove of advantage, and when once a bird had become a plasterer, intelligence, and also haste, might lead it to use whatever came first to hand. Bees will carry oatmeal instead of pollen if the former be put in their way, and birds may be credited with equal adaptability.

After watching blackbirds building, and examining the nest in its various stages of construction, I think it much more likely that the thrush has passed through, and then discarded, a final stage of thatching the nest, than that it has stopped short at the stage of