The book "Biological problem of today: preformation or epigenesis? Foundations of the theory of organic development" by the author Oskar Hertwig is a landmark scientific work devoted to the discussion about the development processes of living organisms. In the book, the author raises an important question about how organisms are formed: are they already programmed at the beginning of their existence (preformation), or does development take place under the influence of external factors (epigenesis). Hertwig argues his position with the support of empirical observations and theoretical calculations, offering the reader a deep analysis and a broad overview of scientific facts. The book opens the reader to the fascinating world of biology and philosophy, provoking thoughts and discussions on the nature of organic development. "The Biological Problem of Today: Preformation or Epigenesis? Foundations of the Theory of Organic Development" is a must-read for anyone interested in biology, the philosophy of science, and the general theory of evolution.