But we went further than this, and saw that there is a second result implied in amphimixis, namely, that the individual character of the germ-plasm is being continually altered by new combinations of the ids contained in it. We inferred from what I believe to be the demonstrated hypothesis that the germ-plasm is composed of ids, that its reduction to half the original mass must mean a reduction of the ids to half the number, and as the ids contain primary constituents which are individually different, this must effect a new arrangement, a new mingling of these individual peculiarities. The reduction of the germ-plasm to half, that is, the diminution of the number of its ids to half, is a phenomenon generally associated with amphimixis, and has been established in the case of all animals which have hitherto been investigated, and of all the most carefully studied plants, and finally, it has been shown to be very probable in unicellular organisms, for the processes of conjugation in Infusorians and many other Protozoa include phenomena very similar to those of reducing division in the higher animals. The prediction made on theoretical grounds has here been verified by observation, and it is obvious that the assumption of ids, that is, of units in the germ-plasm which are handed on from one generation to the succeeding one, involves a reduction of their number in each amphimixis. Without this the number of ids would be doubled at each amphimixis, and would therefore gradually amount to something enormous. We see therefore why this normally recurrent reduction of ids before each amphimixis was established in the course of evolution, and we see that it inevitably involves that a new combination of ids should be associated with each amphimixis. If nothing persists unless it be purposeful, that is, necessary, what is the meaning of the fact that arrangements for amphimixis occur over almost the whole known domain of life, from the very simple organisms up to the highest, in unicellular and multicellular organisms, in plants and animals alike? Why is it that this arrangement has been departed from only in a few small groups of forms, while it occurs everywhere else, in almost every generation, so indissolubly associated with reproduction that it has even been regarded--with a lack of clearness--as itself a form of reproduction, and is even now generally called 'sexual reproduction'? And why is it that in many organisms, especially lowly ones, it is not associated with every reproduction, though it recurs at regular or irregular intervals? Such a universal arrangement must undoubtedly be of fundamental importance, and we have to ask wherein this importance lies. That is the problem to the solution of which we must now apply ourselves.