These brief remarks will perhaps suffice to give some idea of the variety of instinct and habit that prevails in this very interesting genus. Friese observes that the variety of habits in this genus is accompanied as a rule by paucity of individuals of a species, so that in central Europe a collector must be prepared to give some twenty years or so of attention to the genus before he can consider he has obtained all the species of _Osmia_ that inhabit his district. As a prelude to the remarks we are about to make on the leaf-cutting bees of the genus _Megachile_ it is well to state that the bee, the habits of which were described by Réaumur under the name of "l'abeille tapissière," and that uses portions of the leaves of the scarlet poppy to line its nest, is now assigned to the genus _Osmia_, although Latreille, in the interval that has elapsed since the publication of Réaumur's work, founded the genus _Anthocopa_ for the bee in question. _Megachile_ is one of the most important of the genera of the Dasygastres, being found in most parts of the world, even in the Sandwich Islands; it consists of bees averaging about the size of the honey-bee (though some are considerably larger, others smaller), and having the labrum largely developed; this organ is capable of complete inflection to the under side of the head, and when in the condition of repose it is thus infolded, it underlaps and protects the larger part of the lower lip; the mandibles close over the infolded labrum, so that, when the Insect is at rest, this appears to be altogether absent. These bees are called leaf-cutters, from their habit of forming the cells for their nest {52}out of pieces of the leaves of plants. We have several species in Britain; they are very like the common honey-bee in general appearance, though rather more robustly formed. These Insects, like the Osmiae, avail themselves of existing hollow places as receptacles in which to place their nests. _M. albocincta_ frequently takes possession of a deserted worm-burrow in the ground. The burrow being longer than necessary the bee commences by cutting off the more distant part by means of a barricade of foliage; this being done, it proceeds to form a series of cells, each shaped like a thimble with a lid at the open end (Fig. 22, A). The body of the thimble is formed of large oval pieces of leaf, the lid of smaller round pieces; the fragments are cut with great skill from the leaves of growing plants by the Insect, which seems to have an idea of the form and size of the piece of foliage necessary for each particular stage of its work. [Illustration: Fig. 22—Nidification of leaf-cutting bee, _Megachile anthracina_. A, one cell separated, with lid open; the larva (_a_) reposing on the food; B, part of a string of the cells. (After Horne.)]