PREFACE. 
xv 
An author may easily be mistaken in estimating his own 
work. I am well aware that this first outline of a great 
subject is, in parts, very meagre and sketchy; and, though 
perhaps overburthened with some kinds of detail, yet leaves 
many points most inadequately treated. It is therefore with 
some hesitation that I venture to express the hope that I have 
made some approach to the standard of excellence I have aimed 
at ; — which was, that my book should bear a similar relation to 
the eleventh and twelfth chapters of the “ Origin of Species,” as 
Mr. Darwin’s ;c Animals and Plants under Domestication ” does 
to the first chapter of that work. Should it be judged worthy 
of such a rank, my long, and often wearisome labours, will be 
well repaid. 
Makcii, 1876 . 
