How—and the question has often been asked—are the experiences of the infertile females, the workers, transmitted to the germ-plasm? For the workers, it has been contended, being sterile, are incapable of handing on such acquirements: this is so. These workers hold the same position in regard to the species that structures essential to well-being hold in regard to the individual. These last are not under the control of the individual, but are determined by a plus or minus quality in its germ-plasm. The worker-bees are products of the germ-plasm, committed to the care of the queens. Any strain, so to speak, of that germ-plasm which gives rise to defective workers brings about its own extinction, or elimination, sooner or later. Any strain of germ-plasm which contains, so to speak, a spark of that quality which in the individual is expressed by intelligent behaviour, will gain advantages in the struggle for existence. The complex, the extraordinarily complex, behaviour of the worker-bees on any interpretation is still mysterious. This interpretation can be tested only by a reference to the life-history of other social-bees which have attained to a less complexity. This shows us that the sterile worker is not to be regarded as a newly-evolved type so much as an arrested stage of a more complete ancestral condition, and the fact that the worker is potentially a queen is further evidence of this. A clue to many of the more puzzling features presented by the domestic economy of the Hive-bee may be obtained by a study of the life-history of other species of social-bees which have not attained to so high a degree of specialization. The Bumble-bees afford illustrations of the stages through which _Apis mellifica_, the Hive-bee, must have passed.