PREFACE. XV 



An author may easily be mistake u 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 " 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. 



