We are now at the threshold of that system of sexual propagation which has become the rule in all the higher families of animals and in many plants. It may be conceived as originating in the amalgamation of some germ-cell or spore with the original cell which was about to develop into a germ-bud within the body of some individual, and by the union of the two producing a new and more vigorous originating cell which modified the course of development of the germ-bud and of its resulting organism. This organism, having advantages in the struggle for life, established itself permanently with ever new developments in the same direction, which would be fixed and extended in its descendants by heredity, and special organs developed to meet the altered conditions. Thus at length the distinction would be firmly established of a female organ or ovary containing the egg or primitive cell from which the new being was to be developed, and a male organ supplying the fertilising spore or cell, which was necessary to start the egg in the evolutionary process by which it developed into the germ of an offspring combining qualities of the two parents. This is confirmed by a study of embryology, which shows that in the human and higher animal species the distinction of sex is not developed until a considerable progress has been made in the growth of the embryo. It is only however in the higher and more specialised families that we find this mode of propagation by two distinct individuals of different sexes firmly established. In the great majority of plants, and in some of the lower families of animals—for instance, snails and earth-worms—the male and female organs are developed within the same being, and they are what is called hermaphrodites. Thus, in most of the flowering plants the same blossom contains both the stamens and anther, which are the male organ, and the style and germ, which are the female. Another transition form is Parthenogenesis, or virginal reproduction, in which germ-cells, apparently similar in all respects to egg-cells, develop themselves into new individuals without any fructifying element. This is found to be the case with many species of insects, and with this curious result, that those same germ-cells are often capable of being fructified, and in that case produce very different individuals. Thus, among the common bees, male bees or drones arise from the non-fructified eggs of the queen bee, while females are produced if the egg has been fructified.