The shape and size of the nest are exceedingly variable, but it is almost invariably longer than wide, and is fixed to a branch or some similar object. Sometimes it attains considerable dimensions, and has been known to measure a full yard in length. Yet, however large it may be, there is only a single comb, which is set upon the side of the nest next the branch, and, in consequence, has almost all its cells placed in a horizontal direction. In the illustration, the right-hand figure represents the external appearance of the nest, and the central figure shows the manner in which the single comb is set upon the branch. The nest which occupies the left hand of the illustration is made by a species of _Polybia_, and is here given in order to show a remarkable example of similarity in the mode of building adopted by two different insects. In the one case, however, the cells are all fastened by their bases to the branch, but in the other the cells are attached to one common base which is prolonged into a footstalk. There have been lately discovered some very remarkable social nests. Specimens of both these nests may be seen in the entomological department of the museum at Oxford. The first is formed very much like a rather flattened Florence flask, and is hung by the neck from the branch of a tree. It is made of a strong, parchment-like substance, formed by innumerable silken threads woven and matted together into a kind of felt. When it was cut open a most singular sight was exhibited. Nearly the whole of the interior was covered with the pupæ of some butterfly, all hanging by their tails, and many of them suspended to a twig which projected downwards into the nest. Although the nest is barely eight inches in length, a great proportion of which is taken up by the neck, about one hundred pupæ were found in it. At the bottom of the nest is a small and nearly circular aperture, through which the insects could make their way as soon as they escaped from the pupal envelope, and before their wings became extended and hardened. The butterfly which makes this singular nest is a native of Mexico, and is named _Eucheira socialis_. The colour of its wings is dark brown, with an ill-defined white band across them.