INTRODUCTORY. 171 



are likely to understand, without having previously ac- 

 quired that knowledge of the subject under discussion 

 which neither their time nor their opportunities may have 

 allowed them to attain. Secondly, such a preface it is 

 hoped will prepare experienced Entomologists for that 

 chain of reasoning in the following chapters which leads to 

 so many novelties in Natural History ; novelties however 

 that will be found on examination to depend much less on 

 any new observations than probably many in this country 

 ^vill imagine. The observed facts and metaphysical opi- 

 nions hereafter stated I have always indeed preferred to 

 adopt on the assertion of others, as ^vell because I should 

 thus appeal to authority of infinitely greater weight than 

 my own, as in order that I might confine within the 

 narrowest possible bounds that bias towards a favourite 

 hypothesis, from the danger of indulging which I do not 

 flatter myself so much as to fancy that I can be wholly 

 free. A general list therefore of the authors consulted 

 will be inserted in a future volume; and in the mean time, 

 though it is hardly necessary in any work of this age on 

 Natural History to cite the names of Cuvier, Lamarck, 

 Latreille and Savigny, since an appeal to such authorities 

 is always understood, I have peculiar reasons for stating 

 that it is to the labours of these distinguished naturalists 

 that I feel myself more particularly indebted. 



What has been introduced into this Essay of a meta- 

 physical nature may on the first view seem misplaced, from 

 its having to all appearance so little connexion with the 

 prefixed title. To those who may retain this opinion after 

 the perusal of the volume, I can only say that some indul- 

 gence on this head is expected, because observations on 

 machines in motion would be incomplete without some 



