1 9$ The Evolution Hypothesis. 



But it is not enough that the environment initiate 

 the development of structure ; what is begun needs 

 continued causation to carry it forward to future 

 stages. Observation shows that the process is liable 

 to stop short at any point. There are living creatures 

 that are structureless being nothing more than a 

 bundle of cells multiplying by simple fission. There 

 are others slightly more developed living beings 

 which still retain the structureless condition, and 

 make no advance in organization. Others have an 

 organization of the most rudimentary sort and never 

 advance beyond the point at which the ancestral cell 

 stopped short. These lowly forms of life are no more 

 modifiable than the highest. They are as fixed in 

 kind, and are, in reproduction, as true to kind, as the 

 most highly developed species. How then are we to 

 account for the extremely diverse action of the same 

 environment ? 



It may be answered, The environments are not the 

 same. The environment of the fertilized germ-cell in 

 the egg of an eagle, is not identical with that in the 

 egg of an ostrich. But such an answer would not be 

 satisfactory ; for, by hypothesis, there was a time 

 when the germ-cell of what is now an ostrich was 

 identical with the germ-cell of what is now an eagle ; 

 and when two germ-cells of the remote ancestor 

 became differentiated, what ground is there for affirm- 

 ing that they were exposed to dissimilar environ- 

 ments ? We assume the very point in question. But 



