ADAPTATION versus INHERITANCE. 253 
animal and vegetable forms, which, in fact, they have. We 
have, at least, hitherto been unable to discover any other 
formative causes besides these two, and if we rightly under- 
stand the necessary and infinitely complicated interaction 
of Inheritance and Adaptation, we do not require to look 
for other unknown causes for the change of organic forms. 
These two fundamental causes are, as far as we can see, 
completely sufficient. 
Even long before Darwin had published his Theory of 
Selection, some naturalists, and especially Goethe, had as- 
sumed the interaction of two distinct formative tendencies 
—a, conservative or preserving, and a progressive or chang- 
ing formative tendency—as the causes of the variety of 
organic forms. The former was called by Goethe the cen- 
tripetal or specifying tendency, the latter the centrifugal 
tendency, or the tendency to metamorphosis (p. 89). These 
two tendencies completely correspond with the two processes 
_of Inheritance and Adaptation. Inheritance is the centri- 
petal or internal formative tendency which strives to keep 
the organic form in its species, to form the descendants like 
the parents, and always to produce identical things from 
generation to generation. Adaptation, on the other hand, 
which counteracts inheritance, is the centrifugal or external 
formative tendency, which constantly strives to change the 
organic forms through the influence of the varying agencies 
of the outer world, to create new forms out of those existing, 
and entirely to destroy the constancy or permanency of 
species. Accordingly as Inheritance or Adaptation pre- 
dominates in the struggle, the specific form either remains 
constant or changes into a new species. The degree of con- 
_stancy of form in the different species of animals and 
