Introductory. 9 
possible, the whole theory of organic evolution as I 
believe that it will eventually stand. My endeavour, 
therefore, will be to exhibit the general structure of 
this theory in what I take to be its strictly logical 
form, rather than to encumber any of its parts by a 
lengthy citation of facts. Following this method, I 
shall in each case give only what I consider the main 
facts for and against the positions which have to be 
argued ; and in most cases I shall arrange the facts 
in two divisions, namely, first those of largest gener- 
ality, and next’a few of the most special character 
that can be found. 
As explained in the Preface, the present instalment 
of the treatise is concerned with the theory of evolu- 
tion, from the appearance of the Origzz of Species in 
1859, to the death of its author in 1882; while the 
second part will be devoted to the sundry post- 
Darwinian questions which have arisen in the sub- 
sequent decade. To the possible criticism that a 
disproportionate amount of space will thus be allotted 
to a consideration of these post-Darwinian questions, 
I may furnish in advance the following reply. 
In the first place, besides the works of Darwin 
himself, there are a number of others which have 
already and very admirably expounded the evidences, 
both of organic evolution as a fact, and of natural 
selection as a cause. Therefore, in the present 
treatise it seemed needless to go beyond the ground 
which was covered by my original lectures, namely, a 
condensed and connected, while at the same time 
a critical statement of the main evidences, and the 
main objections, which have thus far been publ.shcd 
with reterence to the distinctively Darwinian theory. 
