""The Biological Problem of Today: Preformation or Epigenesis? The Basis of a Theory of Organic Development"" is a book written by Oscar Hertwig in 1896. The book discusses the two competing theories of development in biology: preformation and epigenesis. Preformation is the idea that organisms develop from pre-existing structures, while epigenesis is the idea that organisms develop from a process of gradual differentiation and growth. Hertwig argues in favor of epigenesis and provides evidence to support this theory. He also proposes a new theory of organic development based on epigenesis. The book is a significant contribution to the field of developmental biology and remains relevant today. It is written in a clear and concise style and is accessible to both scientists and non-scientists alike.This scarce antiquarian book is a facsimile reprint of the old original and may contain some imperfections such as library marks and notations. Because we believe this work is culturally important, we have made it available as part of our commitment for protecting, preserving, and promoting the world's literature in affordable, high quality, modern editions, that are true to their original work.