22 INTRODUCTION. 



ent existence, are found to vary ; but this primitive 

 adhesion to a being similar to itself is a rule without 

 exception. The separation of the germ is called 

 generation. 



All organized beings produce their like, otherwise 

 death would be a necessary consequence of life,^and 

 the species must become extinct. 



Organized beings have also the power of repro- 

 ducing certain of their own parts, of which they may 

 happen to be deprived. This power is possessed in 

 various degrees by the different species, and is 

 termed reproduction*. 



The development of organized beings is more or 

 less expeditious, more or less extensive, according 

 as circumstances may be fortuitously more or less 

 avourable. Hence it happens that the resemblance 

 of descendants to their parents can never be perfect ; 

 differences of this description among organized be- 

 ings are what are called varieties. We have no proof 

 whatever that the differences which at present cha- 

 racterize the various living beings are likely to have 

 been the result of circumstances. Everything ad- 

 vanced upon this subject is purely hypothetical, and 

 experience shews us that in the present state of the 

 earth the varieties are confined to very narrow limits, 

 and as far back as we are able to penetrate into an- 

 tiquity, we find no reason to believe that they were 

 evermore extensive-)'. 



* See the Note at p. 17. 



t The author is here speaking with a strict reference to varieties 

 only. 



