The more numerous the rods or the free individual ids in a species are, the more numerous are the possible combinations. Whether all the mathematically possible combinations actually occur is a different question, which I should not like to answer in the affirmative just yet; but in any case the _actual_ number of combinations in a species with many nuclear elements will be greater than in one with few, and in this respect those species in which the ids occur as independent granules will have an advantage over those in which they are combined into rods or bands (idants). These latter, however, afford us a better possibility of deducing the new combinations of the ids, although the idants themselves are not outwardly distinguishable from each other. I must refrain from going into these highly interesting processes in more detail just now. So much is certain, that Nature makes use of _various means_ to bring about the re-combination, and at the same time the reduction of the ids during the two 'reducing divisions.' This is proved by the fact recently established by Montgomery, that in many animal groups reduction results from the _first_ maturing division. Whether it operates at this stage with rings, bands, double rods, X-shaped structures, groups of four (tetrads), and so on, all this serves the same end, the more or less thoroughgoing re-arrangement of the hereditary vital units. I am convinced that new investigations into these processes, if they were undertaken from this point of view, would lead to very important results[8]. It would be important to find out how great the variations are which thus arise, for it is very probable that they differ in degree in the different animal-groups. Even the combination of the ids into rods (idants) indicates that some species may be more conservative than others in maintaining their id-combinations, and that there will be among them a greater tenacity in the hereditary combinations of characters (i.e. of the 'type' of the parents). If we should succeed in penetrating more deeply into these processes we should probably also understand why in certain human families the hereditary characters are transmitted more purely and more tenaciously than those of other families with which they have mingled, and so on. It may well be that the persistence of character is due to the fact that ids which have once combined into rods hold firmly together, for it seems to me in no way impossible that individual differences should occur even in these most delicate processes.