New discoveries in the field of heredity--Mendel--Rediscovery of Mendelian principles--Independence of inheritable characters-- Illustration in the Andalusian fowl--The cause of the ratio-- Verification of the hypothesis--Dominant and recessive-- Segregation in the next generation--Illustrated in guinea-pigs-- Terminology--The theory of presence and absence--Additional terminology--Dominance not always complete--Modifications of dominance--Mendel's own work--Dihybrids--Getting new combinations of characters--Segregations of the determiners--Four kinds of gametes in each sex--The 9:3:3:1 ratio--Phenotype and genotype-- The question of blended inheritance--Nilsson-Ehle's discoveries-- Such cases easily mistaken for true blends--Skin-color in man-- Questionable if real blends exist--The place of the Mendelian factors in the germ-cell--Parallel between the behavior of Mendelian factors and chromosomes--A single chromosome not restricted to carrying a single determiner. IV MENDELISM IN MAN 97 Probably applicable to many characters in man--Difficult to get correct data--A generalized presence-absence formula--Indications of incomplete dominance--Why after the first generation only half the children may show the dominant character--Eye-color in man-- Hair-color--Hair-shape--Irregularities--Digital malformations--Eye defects--Other defects inherited as dominants--Recessive conditions more difficult to deal with--Albinism--Other recessive conditions in man--Breeding out defects--Other inheritable conditions in man. V ARE MODIFICATIONS ACQUIRED DIRECTLY BY THE BODY INHERITED? 121