suspend her architectural labours and to divide her time between the erection of fresh cells and the feeding of the larvæ in those which were first made. Soon, however, her labours become more onerous and more complicated. The larvæ or grubs, which inhabited the first two or three cells, have grown so rapidly that they are fast becoming too large for their pendent cradles. The cells must therefore be enlarged to suit the increased dimensions of the inhabitants. This also is done, each addition being marked by the ridge which has been already mentioned.

Thus, then, the hard-worked mother insect is forced to engage in three distinct labours, namely, the building of new cells, the enlargement of existing cells, and the nurture of the larvæ. A short reference to the illustration will now give the reader a clear idea of the cell-group. Above is a series of completed cells, each occupied by a full-grown larva, one of which is being fed by the mother insect, and below is a series of incomplete cells, each of which has received an egg, but neither of which is fit to sustain the weight of the larvæ. If, however, the nest had been allowed to remain in the forest, instead of being carried off to the British Museum, the five lower cells would have been completed like their more perfect predecessors above.

The observant reader will probably have noticed that from the mouths of several cells a scoop-like projection is seen to issue. These projections have been faithfully rendered by the draughtsman, although they denote a certain imperfection in the specimen. They are evidently the result of hard usage, and show that part of a completed cell has been broken away. As is often the case, the fracture has its value, inasmuch as it shows that the normal form of the cell is hexagonal, and that the angles are quite sharp and firm without needing either pressure or excavation to make them so.

It is much to be regretted that in England there is no representative of this interesting group of insects by which the above-mentioned problem might be solved. We might then know whether males and females belong to the same brood, are nurtured in the same cells, and are of the same size. We might learn whether or not the males are bred in separate establishments divided from the other sex like dicecious plants. As it is, however, we are in ignorance respecting these points, and no

one resident in tropical countries seems to have the energy to conduct a series of experiments which would involve expenditure of time and labour. Travellers and residents in tropical countries are often admirable collectors, but, with few exceptions, are poor observers, except of facts that pass immediately under their observation. They make valuable collections, and record many useful isolated facts; but, unfortunately, they seldom appear able to carry on a series of experiments that would occupy several successive years, and thus we lose much valuable as well as interesting knowledge, and waste much time in trying to discover by inference that which we ought to know from observation.

The last point which will be noticed in connexion with this remarkable cell-group is, that it is perfectly protected from rain. Slight and delicate as is the structure, appearing scarcely thicker than the silver paper with which engravings are guarded, it may be deluged with water without being wetted. Over the whole of the cells the insect contrives to lay a thick coat of some varnishlike substance, which at the same time gives the exterior of the cells a polish, binds them more firmly together, and renders them waterproof. The varnish is nearly transparent, but has a blackish hue, which gives to the whole cell-group a uniformity of aspect which would be wanting if the protecting substance were itself colourless.

The insect is, at first sight, black in colour, as is expressed by its specific title. A closer examination in a more favourable light shows that the true colour is a green so deep as to appear black, but having a perceptible bronze gloss in certain lights. The wings are equally sombre in aspect, looking as if they had been held above the flame of a badly-trimmed lamp, and received all the soot upon their translucent membranes. Indeed, their peculiar colour can only be expressed by the word "smoky."

IT is hardly possible to overrate the wonderful varieties of form that are assumed by the nests of insects,-varieties so bold and so startling that few would believe in the possibility of their existence without ocular demonstration. No rule seems to be observed in them; at all events no rule has, as yet, been discovered by which their formation is guided; neither has

any conjecture been formed as to the reason for the remarkable forms which they assume.

Perhaps, of all the nests in the splendid collection of the British Museum, there are none that cause so much surprise as the wonderful group which is represented in this illustration.

Many persons pass through the room, and even take some notice of the various nests with which they are surrounded, but they seldom notice the peculiarities of this group until pointed out to them. When, however, their attention is directed towards it, they never fail to express their surprise at so curious a structure, and their admiration of the manner in which these natural homes are constructed.

In a recent portion of this work the hexagonal principle of

construction has been mentioned as applied to separate cells of certain hymenoptera, and that no explanation has been given of the mode by which the six-sided cells are made. It is always easier to explode previous theories than to supplant them with one that really explains the enigma; and such is certainly the case with these cells. But when we come to examine the group of nests which are made by an insect called Apoica pallida, the subject takes a wider range, and we are even more hopelessly bewildered than before. In the nests already mentioned the cells are hexagonal, but in these specimens the entire nests assume a form more or less hexagonal, as may be seen by reference to the illustration.

In order to prevent misunderstanding, I must here remark, that the seven nests or cell-groups were not all found adhering to a single branch, as seems to be the case, but that they have been placed near each other in such a manner as to allow of easy comparison, and to show their peculiar form. The large mushroom-shaped nest in the centre, and the small cell-group which occupies the extremity of the bough, appear as they were formed by the insects, but the others have only been arranged for the convenience of comparison.

Even their position has been necessarily altered. Nests of this kind are always placed with the mouths of the cells downward; but, as their peculiar form could not easily be seen if they were allowed to retain their natural position, some of them have been set on their edges, so as to exhibit their outline to the spectator. This is notably the case with that nest which occupies the left hand of the illustration, and which is the most striking of all the specimens.

If the reader will refer to the illustration, he will see that the nests are by no means uniform in size or shape. The larger one, for example, which occupies the centre, rather exceeds ten inches in diameter, while the small nest at the end of the same branch is scarcely half as wide, and the others are of all the intermediate sizes. In shape, too, they differ, some being perfectly hexagonal, others partly so, while others again are nearly circular, though on a careful inspection they show faint. traces of the hexagonal form.

We will now examine these nests, and see where they agree with and differ from each other.

In the first place, their upper surfaces are more or less convex, according to their size; and whether they are circular or hexagonal, the convexity remains the same. This form is evidently intended for the purpose of making them weather-proof; for the rain torrents that occasionally deluge the country would soon wash to pieces any nest whereon the falling drops could make a lodgment. The surface is therefore as smooth as that of the various pasteboard wasps which build in the forests of tropical America.

The upper surface being convex, it naturally follows that the under surface is concave, inasmuch as the cells are of tolerably equal length. In fact, the nests somewhat resemble very shallow basins with very thick sides, and bear an almost startling resemblance to the cap of a very large and very well-shaped mushroom, the central specimen being so fungus-like in form that, if it were laid on the ground in a waste and moist spot, it would soon be picked up as a veritable mushroom. The colour, too, is yellowish brown, and the surface has a kind of semipolish that increases the resemblance.

In the nests of our common wasp, or hornet, the sheets of paper which form the exterior show plainly where each successive flake has been deposited, and the sweep of the insect's jaws is marked distinctly upon the yielding material. Even in the case of the few British species which build pensile nests in the open air, the separate flakes can be distinguished, though they are not so clearly marked as in those homes which are defended from the weather by earth or wood. Our temperate region knows no such sudden vicissitudes of weather as take place near the equator, and there is no need for insect habitations to possess very great strength or powers of resisting water. But in these nests the cover is so beautifully uniform, that no trace of a jaw can be detected upon it.

Agreeing in general appearance, the nests vary somewhat in colour. Of the eight specimens, the generality are of the mushroom-like hue which has already been mentioned. Others, however, rather vary in this respect, and the uniform yellowish brown is pleasingly diversified by patches of red. One of the nests, however, boldly departs from the general uniformity, the surface being not only reddish brown over its whole extent, but as rough as if made of sand-paper, or from the skin of a dogfish.