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 to egg-laying. The division of labour among the two castes of female becomes therefore most complete in the most highly organized society.

Structure.—Details of the structure of bees are given in the article. The feelers (fig. 2, a) are divided into “scape” and “flagellum” as in the ants, and the mandibles vary greatly in size and sharpness in different genera. The proboscis or “tongue” (fig. 2, l) is a hollow organ enclosing an outgrowth of the body-cavity which is filled with fluid, and with its flexible under-surface capable of invagination or protrusion. Along this surface stretches a groove which is surrounded by thickened cuticle and practically formed into a tube by numerous fine hairs. Along this channel the nectar is drawn into the pharynx and passes, mixed with saliva, into the crop or “honey-bag”; the action of the saliva changes the saccharose into dextrose and levulose, and the nectar becomes honey, which the bee regurgitates for storage in the cells or for the feeding of the grubs. The sting (fig. 6, pg, st.) of female bees is usually highly specialized, but in a few genera it is reduced and useless.

Many modifications in details of structure may be observed within the family. The tongue is bifid at the tip in a few genera; usually it is pointed and varies greatly in length, being comparatively short in Andrena, long in the humble-bees (Bombus), and longest in Euglossa, a tropical American genus of solitary bees. The legs, which are so highly modified as pollen-carriers in the higher bees, are comparatively simple in certain primitive genera. The hairy covering, so notable in the hive-bee and especially in humble-bees, is greatly reduced among bees that follow a parasitic mode of life.

Early stages.—As is usual where an abundant food supply is provided for the young insects, the larvae of bees (fig. 3, SL.) are degraded maggots; they have no legs, but possess fairly well-developed heads. The successive cuticles that are cast as growth proceeds are delicate in texture and sometimes separate from the underlying cuticle without being stripped off. The maggots may pass no excrement from the intestine until they have eaten all their store of food. When fully grown the final larval cuticle is shed, and the “free” pupa (fig. 3, N) revealed. The larvae of some bees spin cocoons (fig. 3, co) before pupation.

Nests of Solitary Bees.—Bees of different genera vary considerably in the site and arrangement of their nests. Many—like the common “solitary” bees Halictus and Andrena—burrow in the ground; the holes of species of Andrena are commonly seen in springtime opening on sandy banks, grassy lawns or gravel paths. Our knowledge of such bees is due to the observations of F. Smith, H. Friese, C. Verhoeff and others. The nest may be simple, or, more frequently, a complex excavation, cells opening off from the entrance or from a main passage. Sometimes the passage is the conjoint work of many bees whose cells are grouped along it at convenient distances apart. Other bees, the species of Osmia for example, choose the hollow stem of a bramble or other shrub, the female forming a linear series of cells in each of which an egg is laid and a supply of food stored up. J. H. Fabre has found that in the nests of some species of Osmia the young bee developed in the first-formed cell, if (as often happens) she emerges from her cocoon before the inmates of the later cells, will try to work her way round these or to bite a lateral hole through the bramble shoot; should she fail to do this, she will wait for the emergence of her sisters and not make her escape at the price of injury to them. But when Fabre substituted dead individuals of her own species or live larvae of another genus, the Osmia had no scruple in destroying them, so as to bite her way out to air and liberty.

The leaf-cutter bees (Megachile)—which differ from Andrena and Halictus and agree with Osmia, Apis and Bombus in having elongate tongues—cut neat circular disks from leaves, using them for lining the cells of their underground nests. The carpenter-bees (Xylocopa and allied genera), unrepresented in the British Islands, though widely distributed in warmer countries, make their nests in dry wood. The habits of X. violacea, the commonest European species, were minutely described in the 18th century in one of R. A. F. de Réaumur’s memoirs. This bee excavates several parallel galleries to which access is gained by a cylindrical hole. In the galleries are situated the cells, separated from one another by transverse partitions, which are formed of chips of wood, cemented by the saliva of the bee.

Among the solitary bees none has more remarkable nesting habits than the mason bee (Chalicodoma) represented in the south of France and described at length by Fabre. The female constructs on a stone a series of cells, built of cement, which she compounds of particles of earth, minute stones and her own saliva. Each cell is provided with a store of honey and pollen beside which an egg is laid; and after eight or nine cells have been successively built and stored, the whole is covered by a dome-like mass of cement. Fabre found that a Chalicodoma removed to a distance of 4 kilometres from the nest that she was building, found her way back without difficulty to the exact spot. But if the nest were removed but a few yards from its former position, the bee seemed no longer able to recognize it, sometimes passing over it, or even into the unfinished cell, and then leaving it to visit again uselessly the place whence it had been moved. She would accept willingly, however, another nest placed in the exact spot where her own had been. If the unfinished cell in the old nest had been only just begun, while that in the substituted nest were nearly completed, the bee would add so much material as to make the cell much larger than the normal size, her instinct evidently being to do a certain amount of building work before filling the cell with food. The food, too, is always placed in the cell after a fixed routine—first honey disgorged from the mouth, then pollen brushed off the hairs beneath the body (fig. 7, c) after which the two substances are mixed into a paste.

Inquilines and Parasites.—The working bees, such as have been mentioned, are victimized by bees of other genera, which throw upon the industrious the task of providing for the young of the idle. The nests of Andrena, for example, are haunted by the black and yellow species of Nomada, whose females lay their eggs in the food provided for the larva of the Andrena. According to H. Friese, the relations between the host and the inquiline are quite friendly, and the insects if they meet in the nest-galleries courteously get out of each other’s way. D. Sharp, in commenting on this strange behaviour, points out that the host can have no idea why the inquiline haunts her nest. “Why then should the Andrena feel alarm? If the species of Nomada attack the species of Andrena too much, it brings about the destruction of its own species more certainly than that of the Andrena.”

More violent in its methods is the larva of a Stelis, whose operations in the nest of Osmia leucomelana have been studied by Verhoeff. The female Stelis lays her eggs earlier than the Osmia, and towards the bottom of the food-mass; the egg of the Osmia is laid later, and on the surface of the food. Hence the two eggs are at opposite ends of the food, and both larvae