THE BEGINNINGS OF LIFE. 99 



units' seems to be supported by many facts otherwise 

 inexplicable, and to be altogether in harmony with 

 general biological principles, and with the modern 

 Evolution hypothesis — as opposed to that of Bonnet re- 

 specting the continual unfolding of pre-existing germs. 



We may say, therefore, that ^ inheritance,' acting in 

 the manner above indicated, is the potential conserva- 

 tive agency tending to assimilate the products of re- 

 production to the likeness of the organisms from which 

 they have been produced. But where simple organisms 

 are exposed to changes in their environment, they are, 

 by virtue of these changes, subjected to influences which 

 may be capable of inducing functional and structural 

 modifications. Great differences, however, exist with 

 respect to the degree of variation that may be induced 

 in different organisms within similar periods, under the 

 influence of any given changes in their environments. 

 Changes, which may be almost inoperative in producing 

 a modification of some organisms, may produce profound 

 alterations in others. And, similarly, whilst a very 

 prolonged continuance of altered conditions is needful 

 to effect some organisms, the influence of changed 

 conditions on others is rapid and more or less 

 immediate. 



The greater the differentiation and complexity of any 

 organism, the less is it likely to be influenced by slight 

 or temporary modifications in the ^ conditions ' or influ- 

 ences to which it is subjected. The complexity has been 

 gradually attained, and each part or organ has functions 



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