Attached to the mesothorax in the centre, above and behind, are the scutellum and post-scutellum, which in colouring or form often yield subsidiary generic or specific characters. On each side of the mesothorax in front, above the pectus, or breast, and just below and before the articulation of the anterior wings, there is a small tubercle, or boss, separated from the surrounding integument by a suture, the colouring of which frequently yields a specific character, but its uses are not known. [Illustration: Fig. 13.—Posterior legs: 1, of abnormal bee (_Andrena_); 2, scopuliped normal bee (_Eucera_); 3, parasitic bee (_Nomada_). _a_, coxa; _b_, trochanter, with flocculus; _c_, femur; _d_, tibia; _e_, planta; _f_, spinulæ; _g_, tarsus, with its claws.] The _metathorax_ carries the posterior legs laterally beneath, and in the centre, behind, the abdomen. The posterior legs are the chief organs used by the majority of bees for the conveyance of pollen to store in their cells, or, as in the case of humble-bees or the hive bee, the bee bread for the food for the young, or the requisite materials, in the majority of other bees, for nidification. To this end they are either densely clothed with hair throughout their whole extent,—usually externally only,—or this is limited to the external surface of the posterior shank. In the social bees this shank is edged externally with stiff bristles. In these, as in most of the bees, this limb greatly and gradually expands towards its articulation with the _planta_, or first joint of the tarsus; and this surface, which is perfectly smooth, serves to the social bee as a sort of basket to hold and convey the collected materials. The first joint of the tarsus, or planta, of this leg is also used in the domestic economy of the insect to assist in the same object. In the domestic bee the under side of the posterior plantæ have a very peculiar structure, consisting of a series of ten transverse broad parallel lines of minute dense but short brushes, which are used in the manipulations within the hive. Neither the Queen-bee nor the drone have this structure, and in the humble-bee and scopuliped bees the same joint is uniformly covered with this brush without its being separated into lines.