{12}[Illustration: Fig. 6—A, Worker of the honey-bee (_Apis mellifica_), with pollen plates laden; B, basal portions of a middle-leg (trochanter with part of coxa and of femur) with plumose hairs and grains of pollen; C, one hair bearing pollen-grains.] The hind-legs of bees are very largely used in the industrial occupations of these indefatigable creatures; one of their chief functions in the female being to act as receptacles for carrying pollen to the nest: they exhibit, however, considerable diversity. The parts most modified are the tibia and the first joint of the hind-foot. Pollen is carried by other parts of the body in many bees, and even the hind-leg itself is used in different ways for the purpose: sometimes the outer face of the tibia is highly polished and its margins surrounded by hair, in which case pollen plates are said to exist (Fig. 6, A); sometimes the first joint of the tarsus is analogous to the tibia both in structure and function; in other cases the hind-legs are thick and densely covered with hair that retains the pollen between the separate hairs. In this case the pollen is carried home in a dry state, while, in the species with pollen plates, the pollen is made into a mass of a clay-like consistence.[11] The legs also assist in arranging the pollen on the other parts of the body. The males do not carry pollen, and though their hind-legs are also highly modified, yet the modifications do not agree with those of the female, and their functions are in all probability sexual. The parasitic bees also do not carry pollen, and exhibit another series of structures. The most interesting case in this series of modifications is that found in the genus _Apis_, where the hind-leg of male, female, and worker are all different (Fig. 25); the limb in the worker being highly modified for industrial purposes. This case has been frequently referred to, in consequence of the difficulty that exists in connection with its heredity, for the {13}structure exists in neither of the parents. It is, in fact, a case of a very special adaptation appearing in the majority of the individuals of each generation, though nothing of the sort occurs in either parent.