of individuals of one species is due to the inheritance of sports (Darwin's term). He believed, as written in 1876, that transmutation of species is directly due to the influence of environment. He also wrote, "if every variation is regarded as a reaction of the organism to external conditions, as a deviation of the inherited line of development, it follows that no evolution can occur without a change of the environment". (This is close to the modern use of the concept that changes in the environment can mediate selective pressures on a population, so leading to evolutionary change.) Weismann also used the classic Lamarckian metaphor of use and disuse of an organ. 1882–1895 Weismann's first rejection of the inheritance of acquired traits was in a lecture in 1883, titled "On inheritance" ("Über die Vererbung"). Again, as in his treatise on creation vs. evolution, he attempts to explain individual examples with either theory. For instance, the existence of non-reproductive castes of ants, such as workers and soldiers, cannot be explained by inheritance of acquired characters. Germ plasm theory, on the other hand, does so effortlessly. Weismann used this theory to explain Lamark's original examples for "use and disuse", such as the tendency to have degenerate wings and stronger feet in domesticated waterfowl. 1896–1910 Weismann worked on the embryology of sea urchin eggs, and in the course of this observed different kinds of cell division, namely equatorial division and reductional division, terms he coined (Äquatorialteilung and Reduktionsteilung respectively). His germ plasm theory states that multicellular organisms consist of germ cells containing heritable information, and somatic cells that carry out ordinary bodily functions. The germ cells are influenced neither by environmental influences nor by learning or morphological changes that happen during the lifetime of an organism, which information is lost after each generation. The concept as he proposed it was referred to as Weismannism in his day, for example in the book An examination of Weismannism by George Romanes This idea was illuminated and explained by the rediscovery of Gregor Mendel's work in the early years of the 20th century (see Mendelian inheritance). Experiments on the inheritance of mutilation The idea that germline cells contain information that passes to each generation unaffected by experience and independent of the somatic (body) cells, came to be referred to as the Weismann barrier, and is frequently quoted as putting a final end to the theory of