The author published in his present investigation of the heredity of the human blood group types, Part II, his own theory. The hypothesis he then propounded required as a matter of course a supplementary hypothesis, which, however, was left unstated; hence it may be here supplemented.
The supplementary hypothesis in question is the theory of the “Lethal Factor” put forward by Dyke & Budge. The gamete AB is weak in vitality, and, moreover, some phenomenon yet unexplained today takes place in the perion in which a blood type is formed. From these facts it is assumed that the gamete AB perishes in one generation. This assumption also corresponds to the instances reported by Fujitaka and Ito.