PREFACE. Vll 



prevent a considerable diffusion of the little book 

 in this country and in the United States, nor its 

 translation into more than one foreign language. 

 Moreover Mr. Darwin often urged me to revise and 

 expand the lectures into a systematic popular 

 exposition of the topics of which they treat. I 

 Mve more than once set about the task : but the 

 proverb about spoiling a horn and not making a 

 spoon, is particularly applicable to attempts to 

 remodel a piece of work which may have served its 

 immediate purpose well enough. 



So I have reprinted the lectures as they stand, 

 with all their imperfections on their heads. It 

 would seem that many people must have found 

 them useful thirty years ago ; and, though the 

 sixties appear now to be reckoned by many of the 

 rising generation as a part of the dark ages, I am 

 not without some grounds for suspecting that 

 there yet remains a fair sprinkling even of 

 " philosophic thinkers " to whom it may be a 

 profitable, perhaps even a novel, task to descend 

 from the heights of speculation and go over the 

 A B C of the great biological problem as it was 

 set before a body of shrewd artisans at that remote 

 epoch. 



T. H. H. 



HODESLEA, EASTBOrRXE, 



April 7th, 1893. 



