Preface, vii 
expressed ; but I should like to take this opportunity 
of also expressing my obligations to the students who 
attended the lectures in the University of Edinburgh. 
For alike in respect of their large numbers, their 
keen intelligence, and their generous sympathy, the 
members of that voluntary class yielded a degree of 
stimulating encouragement, without which the labour 
of preparing the original lectures could not have been 
attended with the interest and the satisfaction that I 
found in it. My thanks are also due to Mr. R. E. 
Holding for the painstaking manner in which he has 
assisted me in executing most of the original drawings 
with which this volume is illustrated ; and likewise to 
Messrs. Macmillan and Co. for kindly allowing me 
to reprint—without special acknowledgment in every 
case—certain passages from an essay which they 
published for me many years ago, under the title 
“Scientific Evidences of Organic Evolution. Lastly, 
I must mention that I am indebted to the same firm 
for permission to reproduce an excellent portrait of 
Mr. Darwin, which constitutes the frontispiece. 
G.J.R. 
CHRIST CHURCH, OXFORD, 
April 19th, 1892. 
