Weismann advocated the "germ plasm" theory. According to this, inheritance only takes place by means of the germ cells the gametes, such as egg cells and sperm cells. Other cells of the body (somatic cells or "soma") are not agents of heredity. The effect is one-way: germ cells produce somatic cells, and more germ cells. The germ cells are not affected by anything the somatic cells learn or any ability the body acquires during its life. Genetic information cannot pass from soma to germ plasm and on to the next generation. This is referred to as the "Weismann barrier". This idea, if true, rules out the inheritance of acquired characteristics as proposed by Lamarck.