764 DYNAMICAL GEOLOGY. 



15. Through the excessive multiplication of the natural enemies of the individuals 

 of any species. 



16. Through the excessive multiplication of individuals of a species, so that food fails 

 and famine ensues. 



These and other related causes have been ably discussed by Darwin. 



IV. Causes of Extinction depending on the Successional Relations of Species. 



17. Through whatever means — the above or others — that may have sufficed, with 

 the lapse of time, to produce changes in the specific characters of species : in other 

 words, through progress in the evolution — however carried forward — of the systems 

 of life. 



