vi Prefatory Notice. 



laws of variation and of inheritance by the facts 

 given and discussed. There is also a valuable dis- 

 cussion on classification, as founded on characters 

 displayed at different ages by animals belonging 

 to the same group. Several distinguished natural- 

 ists maintain with much confidence that organic 

 beings tend to vary and to rise in the scale, inde- 

 pendently of the conditions to which they and 

 their progenitors have been exposed ; whilst 

 others maintain that all variation is due to such 

 exposure, though the manner in which the envi- 

 ronment acts is as yet quite unknown. At the 

 present time there is hardly any question in 

 biology of more importance than this of the 

 nature and causes of variability, and the reader 

 will find in the present work an able discussion 

 on the whole subject, which will probably lead 

 him to pause before he admits the existence of an 

 innate tendency to perfectibility. Finally, who- 

 ever compares the discussions in this volume with 

 those published twenty years ago on any branch 

 of Natural History, will see how wide and rich a 

 field for study has been opened up through the 

 principle of Evolution ; and such fields, without the 

 light shed on them by this principle, would for 

 long or for ever have remained barren. 



CHARLES DARWIN. 



