10 INTRODUCTION. 



this primitive adhesion to a similar being, is a rule without 

 exception. The separation of the germ is called generation. 



Every organized being re-produces others that are similar 

 to itself, otherwise, death being a necessary consequence of 

 life, the species would become extinct. 



Organized beings have even the faculty of reproducing, in 

 degrees varying with the species, particular parts of which 

 they may have been deprived this is called \he power of re- 

 production. 



The development of organized beings is more or less rapid, 

 and more or less extended, as circumstances are more or less 

 favourable. Heat, the abundance and species of nutriment, 

 with other causes, exercise great influence, and this influence 

 may extend to the whole body in general, or to certain organs 

 in particular : thence arises the impossibility of a perfect 

 similitude between the offspring and parent. 



Diff'erences of this kind, between organized beings, form 

 what are termed varieties. 



There is no proof, that all the differences which now dis- 

 tinguish organized beings, are such as may have been pro- 

 duced by circumstances. All that has been advanced upon 

 this subject is hypothetical. Experience, on the contrary, ap- 

 pears to prove, that, in the actual state of the globe, varieties 

 are confined within rather narrow limits, and go back as far 

 as we may, we still find those limits the same. 



We are thus compelled to admit of certain forms, which, 

 from the origin of things, have perpetuated themselves with- 

 out exceeding these limits, and every being appertaining to 

 one or other of these forms, constitutes what is termed a spe- 

 cies. Varieties are accidental subdivisions of species. 



Generation being the only means of ascertaining the limits 

 to which varieties may extend, species should be defined, the 

 re-union of individuals descended one from the other, or from 

 common parents, or from such as resemble them, as strongly 

 as they resemble each other. Rut although this definition is 

 strict, it will be seen that its application to particular indivi- 

 duals may be very difficult, vi^here the necessary experiments 

 have not been made. 



