The last portion of the _trophi_, also double, are the mandibles; they articulate on each side with the cheeks; they act laterally, and are variously formed, according to the economy of the insect. In the females they are usually more or less toothed, and are especially broad, curved, and toothed in the artisan bees. In _Apis_ and _Bombus_ they are subdentate. In males they are frequently simply acute, but in some species, especially in _Andrena_, they have a long spine at the base, which points downwards when they are closed. To this sex they appear to be of no use beyond aiding them to stay the wayward caprice or flight of their mistresses; and, although they have an analogical structure in the males of those genera wherein they are much dilated and toothed, yet they do not seem to be at all used by that sex for any purpose but sexual. In the females they are used for the construction of their burrows and nests, and for the purpose of nipping the narrow spurs and tubes of flowers to get at the nectar; and they often nip, whilst seeking pollen, the anthers of the flowers which have not yet burst their receptacles of pollen. These insects must necessarily nicely appreciate the quantity of pollen requisite to the full development of the young insect, and, although we often observe a remarkable difference of size in the individuals of a species, this may rather arise from some defect in the quality of the nutritive purveyance than in its quantity, for instinct would as efficiently provide for this purpose as it unquestionably guides to the collection and storing of the nutritive supplies. Having thus completed the description of the head and of all its attachments, I proceed to— The THORAX, which is divided by sutures into three parts already mentioned above, viz. the _prothorax_, the _mesothorax_, and the _metathorax_. The collar, or upper part of the prothorax, is often very distinct, and even angulated laterally in front, and frequently presents, both in colouring and form, a specific character. At its under portion on each side the anterior legs are articulated. [Illustration: Fig. 11.—Anterior leg. _a_, coxa; _b_, trochanter; _c_, femur, or thigh; _d_, tibia, or shank; _e_, spur and velum; _f_, planta and strigilis; _g_, digitus; _h_, claw; _i_, pulvillus, or cushion.]