PREFACE 
SEVERAL years ago Lord Rosebery founded, in 
the University of Edinburgh, a lectureship on * The 
Philosophy of Natural History,’ and I was invited by 
the Senatus to deliver the lectures. This invitation 
I accepted, and subsequently constituted the material 
of my lectures the foundation of another course, which 
was given in the Royal Institution, under the title 
“ Before and after Darwin.” Here the course extended 
over three years—namely from 1888 to 1890. The 
lectures for 1888 were devoted to the history of biology 
from the earliest recorded times till the publication of 
the “Origin of Species” in 1859; the lectures for 
1889 dealt with the theory of organic evolution up to 
the date of Mr. Darwin's death, in 1882; while 
those of the third year discussed the further develop- 
ments of this theory from that date till the close of 
the course in 1890. 
It is from these two courses-—which resembled each 
other in comprising between thirty and forty lectures, 
but differed largely in other respects—that the pre- 
sent treatise has grown. Seeing, however, that it has 
