So far there seems to be but little differentiation between Hunger and Love. Love is only a special hunger which leads cells to obtain nourishment from other cells of the same species; and generation or reproduction in these early stages, being an inevitable accompaniment of growth, follows on the satisfaction of love just as it follows on the satisfaction of hunger. Rolph’s words on the relation of these two impulses (quoted by Geddes and Thompson) are very suggestive. He says:—“Conjugation occurs when nutrition is diminished.... It is a necessity for satisfaction, a growing hunger, which drives the animal to engulf its neighbor, to ‘isophagy.’ The process of conjugation is only a special form of nutrition, which occurs on a reduction of the nutritive income, or an increase of the nutritive needs.” And so far there is no distinction of sex. It is true there may be sex in the sense of union or fusion between two individuals; but there is no distinction of sex, in the sense of male and female. In the Protozoa generally there is simple union or conjugation between cells, which, as far as can be observed, are quite similar to each other. It is a union between similars; and it leads to growth and reproduction. But both union and reproduction at this early stage exist quite independently of any distinctive sex-action, or any differentiation of individuals into male and female. At a later period, however, Sex comes in. It is obvious that for growth (and reproduction) two things are necessary, which are in some degree antagonistic to each other—on the one hand the pursuit and capture of food, which means _activity_ and force, and on the other hand the digestion and assimilation of the food, which means _quiescence_ and passivity. And it seems that at a certain stage—in general, when “animals” have already been formed by the conjunction of many protozoic cells in co-operative colonies—this differentiation sets in, and some individuals specialize towards activity and the chase, while others (of the same species) specialize towards repose and assimilation. The two sets of qualities are clearly only useful in combination with each other, and yet, as I have said, they are to some degree contrary to each other; and therefore it is quite natural that the two corresponding groups of individuals should form two great branches in each race, diverse yet united. These two branches are the male and female—the active, energy-spending, hungry, food-obtaining branch; and the sessile, non-active, assimilative and reproductive branch. And by the division of labor consequent on the formation of these two branches the whole race is benefited; but only of course on condition that the diverse elements are reunited from time to time. It is in the fusion of these elements that the real quality and character of the race is restored; and it is by their fusion that development and reproduction are secured.