TREVIRANUS. 187 



The ' Urbild,' or type, was composed of the internal 

 original common characters, or, as we should say, 

 the ' stem characters,' lying at the base of all forms, 

 and these original structures were preserved by 

 heredity. 



The preservation of this type was opposed by 

 a continuous progressive development, and this 

 was necessitated by the relations of the organism to 

 the outer world. The former, or type, is the cen- 

 tripetal structural force, or specification ; while the 

 latter, or progressive development, is the centrifugal 

 structural force, or metamorphosis. Goethe prized 

 highly the conception of these two opposed forces, 

 which we now know as Heredity and Variation, or 

 Inheritance and Adaptation. Morphology was 

 Goethe's favourite study, and upon transformation 

 depended all his ideas of the Descent theory. Phy- 

 letic series, and the methods of ascertaining them, 

 were wholly unknown to him, but structural series, 

 or the modifications of a primitive type or arche- 

 type, exhibited successively in the lower and higher 

 types of plants and in the lower and higher types 

 of animals, were clearly perceived, and, as we have 

 seen above, they led Goethe to a thoroughly philo- 

 sophical interpretation of structures in all stages of 

 Evolution, in the three phases of Development, Bal- 

 ance, and Degeneration. 



GOTTFRIED REINHOLD TREVIRANUS (1776-1837), a 

 prominent German naturalist and contemporary of 

 Lamarck and Goethe, has the distinction of defin- 



