The volume analyzes regenerative phenomena across plants and animals, relating budding, fission, autotomy and tissue replacement to a germ-plasm framework that posits accessory idioplasm in reparative cells. It examines inheritance and contests transmissibility of acquired functional modifications, considers opposing objections, and develops the idea of germinal selection during development. It discusses the maturation of germ-cells, the biogenetic law, and the structural role of amphimixis in heredity. Reproductive variations including in-breeding, parthenogenesis and asexual reproduction are evaluated, and environmental influences, isolation, and mechanisms of speciation are explored. The work closes by treating species origin, extinction, and the question of spontaneous generation.