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Rh except perhaps sparrows—not counting poultry of course. Already the terns have gone a good deal further than the guillemots, for they not only show the liveliest interest in the common progeny, and combine together for their defence, but there is also, I believe, a good deal of communistic feeding amongst them. Other birds, perhaps, have gone further still.

In what does the interest taken by a bird—let us say by one of these guillemots—in a chick which is not its own originate? Does not the sight of it arouse, by association of ideas, all those feelings which, but shortly before, its own chick was daily arousing? And if this be so, does it not in a manner mistake it for its own? It would be interesting, were something to happen to the parents of this little chick, to see if it would be fed and taken care of by any of the other birds on the ledge. If it were to be, I should be inclined to think this the reason of it. That one bird (or pair of birds) should foster the young of another, knowing all the while that it was another's, and not its own, seems to me very unlikely. There must be some confusion of thought. By association of ideas the stranger chick would excite in the stranger bird the feelings proper to rearing, whilst at the same time supplying in itself the proper object for their translation into act. When once this point had been reached, the foster-parent, if it did not look upon the chick as its own, would have—always supposing it to be one of these guillemots here—to retain a clear recollection of the chick that it had