45'6 ON THE TRIBES 



own division of them, and this is not much, the Systema 

 Entomologicd would have been nearly as consonant with 

 nature as it is now the reverse. Any principle of dis- 

 tribution, whether wings or tarsi, antenna? or maxillee, 

 though perhaps not always convenient, is in itself good ; 

 the difference in the effect consists wholly in the method 1 

 of using it, and there is no principle so good as not to be-' 

 come worse than useless by being applied improperly. Re- 

 lations of analogy themselves seem to be of little use in 

 prescribing exact limits to a group. Nay, when we em- 

 ploy such relations as absolute characteristics of all the 

 contents of a group, then the most natural of characters 

 become artificial. Thus Metamorphosis constitutes the 

 basis of the analogy which reigns between the correspond- 

 ing orders of Mandibulata and Haustellata. Yet if it be 

 used to circumscribe these orders with precision, the ex- 

 tremity of some of the most natural groups, such as the 

 Diptera, will be divided from those types to which they 

 evidently are referable. Hence we may conclude that the 

 variation of Metamorphosis is only an index of the series 

 of affinity, and not a principle by which the orders have 

 been strictly circumscribed. 



Notwithstanding the importance in Zoology of this 

 maxim of variation, it has never that I know of been clearly 

 expressed; and, as it has certainly never been acted upon, 

 we may doubt that it can have been distinctly under- 

 stood. The only author in whose works I have been able 

 to trace a vestige of it, is that great philosopher whose 

 merits I have occasionally canvassed with severity, both 

 for the sake of benefit to science and of justice to Ray, — 

 most assuredly not from any unworthy wish to detract from, 



