As is well known this does happen not infrequently, although it is difficult or impossible to demonstrate it precisely. In plant-hybrids proof is easier, and it has been established that by far the greater number of hybrids maintain a medium between the characters of the two ancestral species. This proves that our assumption of equal strength of the ids of both species must be correct in general, for we know definitely in this case, as I shall show later, that the paternal and the maternal ids are equivalent as regards the characters of the species. This is the case, for instance, with the hybrids between the two species of tobacco-plant, _Nicotiana rustica_ and _N. paniculata_, which were reared by Kölreuter as far back as the eighteenth century, and which then, as now, maintained a fairly exact medium between the two ancestral species, and did so in all the individuals. Both species thus strive to stamp their own character on the young plant, and in both the hereditary power is equally great; in both it is contained in the same number of ids, that is, in the half, for both kinds of sex-cell have undergone reducing division. We have here, then, strict proof that the half number of ids suffices to reproduce in the offspring the type of the species, or, more generally, of the parents. If we apply these results to the inheritance of individual differences in Man, we may say, that those germ-cells, to which at the reducing division the same combination of ids has been handed on as that which already determined the type of the parent, will endeavour to impress this image again on the child. If a female cell of this kind combine with a male which likewise contains the facies-combination of the parent, in this case the father, the same thing will happen which we described in the case of the plant-hybrids, that is, a medium form between the type of the two parents will arise. Not infrequently, however, there is a marked preponderance of the one parent in the type of the child, and we have to inquire whether the theory gives us any help with regard to such a case. One might be inclined to assume a difference in the determining power of the paternal and maternal ids, but if we cannot show to what extent and for what reason this power may be different such an assumption remains rather an evasion than an explanation. Moreover, it would not always apply to the conditions in Man, for if, for instance, the ids of a particular mother were in general stronger than those of the father, all the children of the pair in question would necessarily take after the mother; but it happens not infrequently that one child resembles the father preponderantly, and another the mother. Moreover, the ids pass continually from the male to the female individual, and conversely, by virtue of the continuity of the germ-plasm, so that the idea that sex can have anything to do with the relative strength of the ids is altogether erroneous.