Who, by a mere glance, could imagine the materials that the little bird called the vireo employs in building her peculiar nest? The reader will remember how we pulled one of those nests apart, and what strange materials we found woven in its fabric.[2] But they were hardly more surprising than we may discover within this sly cocoon if we dissect it. Now, to begin with, a true cocoon is not solid to the core, as this one evidently is as we press it between our fingers, nor can you pinch off a tuft of gray hair from the surface of an ordinary cocoon when you will. True, there are some cocoons into whose silk meshes the caterpillar weaves the hair of its body, but the felt thus formed is only a shell, and is intermeshed with silken webs, and one pinch alone will open up the hollow interior and show us the caterpillar or chrysalis within. Such, for instance, is the little brown winter snuggery of the woolly-bear caterpillar which we all know, and whose prickly cocoons may be found beneath stones and logs in the fields. [2] See "Sharp Eyes," But what do we find in these cocoons that we now have before us? Not only is there no vestige of silk to be seen, but there are hairs enough in this single cocoon to have supplied a hundred caterpillars, while we look in vain for any sign of the spinner within. Indeed, there is no within; pinch after pinch reveals nothing but the same gray felt. We are now a quarter of an inch below the surface, when another pinch brings with it a small mass of white specks like crumbs intermingled with the hair, and in the hollow thus deepened we observe a shiny white object like ivory, with a minute ball at its tip. It certainly looks like a tiny bone. We impatiently break open the cocoon, when we see in truth a bone--indeed, a compact mass of bones from some very small animal, whose identity we may guess from the mouse-color of the felt. Here is the femur of a field-mouse--two of them--also a part of the fibula, and a dozen or more other bones. Breaking asunder the mass further, we find a few tiny teeth; and as we continue the process in the remaining two specimens, we bring to light parts of the skull, ribs, and vertebræ. A strange "cocoon" indeed. A further examination of the remaining specimens disclosed similar ingredients, until the entire mass presented a collection somewhat like that shown in my illustration. I well remember my first encounter with the queer specimens, and what mysteries they were, though the "cocoon" idea had never suggested itself to me, the felted mass having been found in a disintegrated state.