This nest is a beautiful piece of bird architecture. In a walk in search of one only a day or two ago I procured one, which is now before me. It was built in the fork of an elder-bush, to which it was moored by strips of fine bark and cobweb, its downy bulk being composed by a fitted mass of fine grass, willow cotton, fern wood, and other similar ingredients. It is about three inches in depth, outside measurement. But this depth greatly varies in different specimens. Our next specimen may afford quite a contrast, for the yellow warbler occasionally finds it to her interest to extend the elevation of her dwelling to a remarkable height. On page 50 is shown one of these nests, snugly moored in the fork of a scrub apple-tree. Its depth from the rim to the base, viewed from the outside, is about five inches, at least two inches longer than necessity would seem to require, and apparently with a great waste of material in the lower portion, as the hollow with the pretty spotted eggs is of only the ordinary depth of about two inches, thus hardly reaching half-way to the base. Let us examine it closely. There certainly is a suspicious line or division across its upper portion, about an inch below the rim, and extending more or less distinctly completely around the nest. By a very little persuasion with our finger-tip the division readily yields, and we discover the summit of the nest to be a mere rim--a top story, as it were--with a full-sized nest beneath it as a foundation. Has our warbler, then, come back to his last year's home and fitted it up anew for this summer's brood? Such would be a natural supposition, did we not see that the foundation is as fresh in material as the summit. Perhaps, then, the bird has already raised her first spring brood, and has simply extended her May domicile, and provided a new nursery for a second family. But either supposition is quickly dispelled as we further examine the nest; for in separating the upper compartment we have just caught a glimpse of what was, perhaps only yesterday, the hollow of a perfect nest; and, what is more to the point of my story, the hollow contains an egg--perhaps two, in which case they will be very dissimilar, one of delicate white with faint spots of brown on its larger end, the putting of the warbler, the other much larger, with its greenish surface entirely speckled with brown, and which, if we have had any experience in bird-nesting, we immediately recognize as the mischievous token of the cow-bird. We have discovered a most interesting curiosity for our natural-history cabinet--the embodiment of a presumably new form of intelligence in the divine plan looking to the survival of the fittest. It is not known how many years or centuries it has taken the little warbler to develop this clever resource to outwit the cow-bird. It is certain, however, that the little mother has got tired of being thus imposed upon, and is the first of her kind on record