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10 The vexed question as to the inheritance of acquired characters is still undecided. Weismann's theories of Heredity and of Organic Evolution have forced biologists to distinguish at least theoretically between those characters which are congenital or inborn and those characters which are acquired by each individual in consequence of its own peculiar experience. Acquired characters are those that are impressed on the organism by the direct action of the environment or which arise as a result of the use and disuse of parts. The old view was that the difference in question was merely one of degree, and not one of kind. The differences in degree related to the fullness and certainty with which the character was inherited. But acquired characters might in time, if continuously developed in each individual through many succeeding generations, become congenital. There was thus no essential difference between them. But this is just the point which Weismann has challenged. According to his theory of Heredity there is a great difference between acquired and congenital characters. The one can never pass into the other. It was in 1883 that Weismann first gave to the world his theory of the Continuity of Germ Plasm. This is taken to be the material basis of heredity and is handed down from generation to generation. Changes produced