SUMMARY OF ' PHILOSOPHIE ZOOLOGIQUE; 293 



entirely upon our relations to the surroundings in which 

 we habitually exist ; we shall have occasion, therefore, 

 to see how great is the effect of environment upon 

 organization. 



" But for our having domesticated plants and animals 

 we should never have arrived at the perception of this 

 truth ; for though the influence of the environment is 

 at all times and everywhere active upon all living 

 bodies, its effects are so gradual that they can only be 

 perceived over long periods of time.* 



" Taking the chain of life in the inverse order of 

 nature — that is to say, from man downwards — we 

 certainly perceive a sustained but irregular degradation 

 of organism, with an increasing simplicity both in 

 organism and faculties. 



" This fact should throw light upon the order taken 

 by nature, but it does not show us why the gradation 

 is so irregular, nor why tVoughout its extent we find 

 so many anomalies or digressions which have apparently 

 no order at all in their manifold varieties.f The ex- 

 planation of this must be sought for in the infinite 

 diversity of circumstances under which organisms have 

 been developed. On the one hand, there is a tendency 

 to a regular progressive development j on the other, 

 there is a host of widely different surroundings which 

 tend continually to destroy the regularity of develop- 

 ment. 



" It is necessary to explain what is meant by such 

 expressions as ' the effect of its environment upon the 

 form and organiz&tion of an animal.' It must not be 

 * 'Phil. Zool.,' torn. i. p. 221. f Page 222. 



