80 DEVELOPMENT AND HEREDITY. 



properties of the "physical basis of life." Some 

 have rather vaguely imagined that this capacity 

 for development was something acquired by natural 

 selection, or that it had originated somehow in the 

 same manner as the generic or class characteristics 

 originate. This supposition, however, lies beyond 

 the limits of legitimate assumption. For if we 

 accept any theory of evolution, we must believe the 

 capacity for development is universal in living 

 matter and co-extensive with life itself. The facts 

 warrant this belief, for even the simple growth of 

 the Protamoeba implies some change and adaptation 

 to the requirements of its increasing size, — a change 

 which is development. This capacity for develop- 

 ment, — for growth and change and constant repe- 

 tition, — ^can be expressed in terms of other and 

 perhaps more familiar phenomena, which may give 

 us more definite ideas of its action, and of the part 

 it plays in determining the particular directions of 

 evolution. It may be regarded as a peculiar im- 

 pressionability of living matter under the action of 

 various forces. 



We have already got some insight into the 

 nature of the action of forces, and their effects upon 

 matter in general : also we have observed the effects 

 of forces of the environment upon living matter. 

 We have seen that all the energy displayed by 



