x PREFACE 



and formation of its rocks, deserts, plains, moun- 

 tains and elevated plateaus, from the wealth or 

 want of vegetation with its lights and shadows, from 

 its climatic conditions, even from the food which it 

 furnishes, is constantly exerting and raining down 

 modifying influences upon the species that by its 

 migration has newly come under it, and is changing 

 in a uniform manner all the individuals of the species, 

 so that no single individual can escape from its 

 established specific bond. 



Lamarck held, and rightly held, that under the new 

 environment into which a migrated species was brought 

 certain changes in its habits must take place, so as 

 to call into play new functional activities, and entail 

 the suspension of some old functions. Thus certain 

 structural elements would be developed, while others 

 from want of use would become atrophied and dwindle 

 into rudimentary proportions. It was his belief also, 

 whether rightly or wrongly I cannot say, that this 

 modifying potency of changed external conditions was 

 sufficient to account for the differentiation of all living 

 organisms into the diverse forms which now exist 

 upon the surface of the globe. 



No reasonable doubt, in my opinion, can be enter- 

 tained that to the modifying influence of changed 

 external conditions are due all the differentiations 

 that exist between the several species that have been 

 derived from a common ancestor, to wit, the generic 

 form which was the origin of the family to which all 

 the related species belong. 



