INTRODUCTION, 23 



We are therefore obliged to admit that certain 

 forms have been perpetuated since the origin of 

 things, without exceeding these limits. All the in- 

 dividuals belonging to any one of these forms con- 

 stitute what is termed a species. The varieties, as 

 we have seen, are accidental ramifications of the 

 species. 



As generation is the only method by which we 

 can ascertain the degrees to which the varieties may 

 extend, we may define the species to be an assem- 

 blage of individuals descended from common pa- 

 rents, who bear the same degree of resemblance to 

 them as they do to each other. But, though this 

 definition be rigorously correct, it is easy to perceive 

 that its application to any given individuals must be 

 attended with considerable difficulty, when we are 

 deprived of the light of observation and experience. 



By way of recapitulation, we may observe that ab- 

 sorption, assimilation, exhalation, development, and 

 generation are the functions common to all living 

 bodies; birth and death the universal limits of their 

 existence ; a porous contractile texture, containing 

 within its laminee moveable liquids or gas, the ge- 

 neral essence of their structure ; substances almost 

 all convertible into liquids or gas, and combinations 

 capable of mutual transformation into either of these, 

 form the basis of their chemical composition. Fixed 

 forms, perpetuated by generation, distinguish their 

 species, determine their inferior functions, and ap- 

 portion to each its destined part in the great theatre 

 of the universe, These forms neither produce or 



