A series of university lectures presents a unified account of heredity and its place in evolution, proposing a continuous germ-plasm made of discrete hereditary determinants aggregated into higher units and arguing that selection operates on these germinal elements rather than by acquired, Lamarckian transmission. The work reviews cellular and reproductive discoveries—chromosomes, mitosis and the centrosome, fertilization, and gametic maturation—to explain reduction during gametogenesis and the mixing of hereditary material. It develops the idea of germinal selection complementing natural selection and assembles empirical and theoretical arguments into a synthetic, accessible presentation for scientifically informed readers.