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 the 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. 
Differences 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. 
Weare 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- 
cles. 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. But although this definition is 
» strict, it will be seen that its application to particular indivi- 
duals may be very diflicult, where the necessary experiments 
have not been made. 
4 
by 
