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Rh general principles by the female blackbird, and she found it in the spreading network of rootlets, belonging to water-loving plants that grew in little rills and ditches, near about her bosky brakes. But to this, mud clung, and, in consequence, there came to be a good deal of the latter in the cup of the nest. Something must be done with it. She began to daub and press it, and, as she became, gradually, more and more a plasterer, mud seemed more and more the proper sort of material to use, till, at last, she sought it for itself alone, utilising the fibres which bound it together, and which had, at first, been what, alone, she sought, as a means of conveying it. But when the mud, thus brought, had been thoroughly smoothed and plastered, so that the nest seemed perfect and "a thing complete," like the thrush's, there would still be something more to be done, for she—our hen blackbird—had always been accustomed to work in stages, and the final or grass-thatching stage had not yet been entered upon. Therefore, she would cover up and entirely conceal all her fine plaster-work, so that no one, seeing the finished nest, would imagine that it existed in any part of it. But will she always do this? I cannot think it, for she is a bird of sprightly intelligence, and I believe that, like the thrush, she will some day find out that the neatly-plastered cup of mud does quite well enough to lay her eggs in, and that the further labour of thatching it with grass can be very well dispensed with. Any saving of time or of labour must be of advantage to a species in the struggle for existence, and those birds who thatched their nests more thinly would be enabled to lay their eggs sooner, and thus rear more offspring. In this way, as well as on the "least action"