Die Perigenesis der Plastidule

Ernst Haeckel's "Die Perigenesis der Plastidule" (1876) proposed a theory of heredity based on molecular movement. Haeckel theorized that "plastidules," hypothetical ultimate units of protoplasm, possessed an undulatory motion that influenced inherited traits. He suggested that external conditions could affect this motion, thereby impacting heredity. This work was part of Haeckel's broader efforts to explain biological phenomena through evolutionary principles and molecular mechanisms, though the concept of plastidules and their specific function in heredity is not supported by modern science. Haeckel is also known for his "biogenetic law," which posited that individual development recapitulates species evolution, a concept that has since been largely discredited.123