In the light of these facts, it is utterly unreasonable to regard the thymus as a practically useless rudiment inherited from the lower vertebrates. “That they have an important function in the young animal,” says Albert Mathews, “can hardly be doubted.” (“Physiological Chemistry,” 1916, p. 675.) In fact, the peculiar nature of their development in the young and their atrophy in the adult forces such a conclusion upon us. The thymus, therefore, is, in all probability, an ontogenetic, and not a phylogenetic, rudiment. It might conceivably be exploited as a biogenetic recapitulation of a reptilian stage in man, just as the so-called fish-kidney of the human embryo is exploited for evolutionary interpretation. The principles by which such a view may be refuted have been given previously. But, in any case, it is folly to interpret the thymus as a rudiment in the racial, rather than embryonic sense. Moreover, the possibility of an ontogenetic interpretation of rudiments must not be restricted to the thymus, but must be accepted as a general and legitimate alternative for the phylogenetic interpretation. In the last place, it remains for us to consider the Darwinian argument, based upon so-called rudimentary organs, from the standpoint of the science of genetics. Darwin, as we have remarked elsewhere, was ignorant of the non-inheritability of those inconstant individual variations now known as fluctuations. He was somewhat perplexed, when Professor L. Meyer pointed out the extreme variability in position of the “projecting point” on the margin of the human ear, but he still clung to his original contention that this “blunt point” was a surviving vestige of the apex of the pointed ears found in donkeys and horses, etc. “Nevertheless,” he says, “in some cases my original view, that the points are vestiges of the tips of formerly erect and pointed ears, still seems to be probable.” (“Descent of Man,” 2nd ed., ch. I, p. 34.) Darwin, as Ranke points out, was mistaken in homologizing his famous “tubercule” with the apex of bestial ears. “The acute extremity of the pointed animal ear,” says this author, “does not correspond to this prominence designated by Darwin, but to the vertex of the helix.” (“Der Mensch,” II, p. 39.) The feature in question is, moreover, a mere fluctuation due to the degree of development attained by the cartilage: hence its variability in different human beings. In very extreme cases, fluctuations of this sort, may be important enough to constitute an _anomaly_, and, as anomalies are often interpreted as atavisms and reversions to a primitive type, it may be well to advert to this subject here.