I must not, however, spend much time over this so-called 'asexual' reproduction by budding and division, because it does not suggest any way by which we may penetrate more deeply into the processes of inheritance, and we may be content if we can bring them into harmony with other theoretical views which we deduce from other phenomena. These forms of reproduction were long regarded as the oldest and the simplest, and it is only since the time of Francis Balfour that the conviction has gradually gained ground that this cannot be so, but that they are rather secondary methods of multiplication in the Metazoa and Metaphyta, which therefore rest on a very complex basis. We have seen that the germ-cells made their appearance along with the multicellular body, and the step from _Pandorina_ to _Volvox_ is as small a step as can be well imagined. It is thus proved that the oldest mode of multiplication among multicellular organisms was that through germ-cells, at least along this line of evolution. _Volvox_ does not reproduce by dividing, or by the development of buds from any part of the spherical colony of cells. What is known as budding among single-celled organisms is only an unequal cell-division, and has nothing but its external appearance in common with the budding of higher plants and animals. The latter, therefore, is something new, of later and independent origin; _the primitive mode is reproduction by unicellular germs_. LECTURE XIV REPRODUCTION BY GERM-CELLS. Historical--Differentiation of germ-cells into male and female--Pandorina--Volvox--Sperm-cells and ova in Algæ--Zoosperm form of the male germ-cells--Zoosperms of the Barnacles--Adaptation of the sperm-cells to the conditions of fertilization--Daphnids--Spermatozoa in different animal groups--Their minute structure--Form and structure of the egg-cell--Adaptation of the ovum to given conditions--Dimorphic ova in the same species--Nutritive cells associated with egg-cells--Complex structure of the bird's egg. IF we now turn to the reproduction of the Metazoa and Metaphyta by means of germ-cells we find that a great number of lowly plants produce germ-cells which require nothing more for the development of a new plant beyond certain favourable external conditions, above all, moisture and warmth. Such, for instance, are the 'spores' of the ferns, which are formed on the under surface of the fronds in little clusters of a brown or yellow colour, easily visible to the naked eye. These spores are individually very small, so that thousands go to form one spore-cluster or sporangium, and millions of spores are given off annually by a single fern. Each spore is a germ-cell enclosed in a protective capsule, and may, if carried by the wind to a spot favourable to germination, become a young plant, the so-called prothallium, from which the fern-plant proper subsequently develops.