The habitations of the insects which we have just described consist of growing leaves, bent, rolled, or pressed together, and fixed in their positions by silken threads. But there are other habitations of a similar kind, which are constructed by cutting out and detaching a whole leaf, or a portion of a leaf. We have already seen how dexterously the upholsterer-bees cut out small parts of leaves and petals with their mandibles, and fit them into their cells. Some of the caterpillars do not exhibit quite so much neatness and elegance as the leaf-cutting bees, though their structures answer all the purposes intended; but there are others, as we shall presently see, that far excel the bees, at least in the delicate minutiæ of their workmanship. We shall first advert to those structures which are the most simple. * * * * * Not far from Longchamps, in a road through the Bois de Boulogne, is a large marsh, which M. Réaumur never observed to be in a dry state even during summer. This marsh is surrounded with very lofty oaks, and abounds with pondweed, the water-plant named by botanists _potamogeton_. The shining leaves of this plant, which are as large as those of the laurel or orange-tree, but thicker and more fleshy, are spread upon the surface of the water. Having pulled up several of these about the middle of June, M. Réaumur observed, beneath one of the first which he examined, an elevation of an oval shape, which was formed out of a leaf of the same plant. He carefully examined it, and discovered that threads of silk were attached to this elevation. Breaking the threads, he raised up one of the ends, and saw a cavity, in which a caterpillar (_Hydrocampa potamogeta_) was lodged. An indefatigable observer, such as M. Réaumur, would naturally follow up this discovery; and he has accordingly given us a memoir of the pondweed tent-maker, distinguished by his usual minute accuracy. In order to make a new habitation, the caterpillar fastens itself on the under side of a leaf of the _Potamogeton_. With its mandibles it pierces some part of this leaf, and afterwards gradually gnaws a curved line, marking the form of the piece which it wishes to detach. When the caterpillar has cut off, as from a piece of cloth, a patch of leaf of the size and shape suited to its purpose, it is provided with half of the materials requisite for making a tent. It takes hold of this piece by its mandibles, and conveys it to the situation on the under side of its own or another leaf, whichever is found most appropriate. It is there disposed in such a manner that the under part of the patch--the side which was the under part of the entire leaf--is turned towards the under part of the new leaf, so that the inner walls of the cell or tent are always made by the under part of two portions of leaf. The leaves of the potamogeton are a little concave on the under side; and thus the caterpillar produces a hollow cell, though the rims are united.