THEORY OP REPRESENTATION. 237 



discovered, it was often most erroneously applied. The 

 result of our researches in following up this law will 

 now be given, 



(292.) No law of the natural system is more calcu- 

 lated to keep in check the ardour of imagination than 

 this. So numerous are the resemblances between ob- 

 jects, that, without a better guide than the return of a 

 series into itself, we may form circles ad infinitum 

 under the idea that they are natural, when, in truth, they 

 are artificial. We could even cite many instances where, 

 by the help of much ingenuity, parallel relations of 

 analogy between artificial groups have been made out, 

 and where, in truth, the whole theory has been mis- 

 applied. But when, superadded to these, we apply the 

 theory of representation in all its bearings, as a third 

 test to the accuracy of our groups, it is next to impos- 

 sible that we should err or violate the series of nature. 

 It is, in fact, as we have elsewhere demonstrated*, 

 " the only certain test of a natural group." This will 

 be evident when we exemplify the theory by a reference 

 to acknowledged facts. 



(293.) The class of Birds, as being that which of all 

 others in the animal kingdom has been most analysed, is, 

 in consequence, best calculated for our present purpose. 

 Every natural group, as we have seen (285.), contains re- 

 presentations of the divisions composing a neighbouring 

 group. Thus the tribes of the order Rasores f repre- 

 sent, by analogy, the tribes of the order Insessores; and 

 these tribes, in a similar way, represent the primary 

 orders of birds. Now this principle pervades every 

 natural group, whatever may be its value, or size, or 

 denomination. It extends not only to orders, tribes, 

 and families, but even to genera and sub-genera. So 

 that, if a sub-genus is sufficiently numerous in species, 

 it will contain types of representation of the remaining 

 sub-genera composing the entire genus, and, conse- 

 quently, of every natural division in the whole class of 



* North. Zool. f See Linn. Trans. voL xvi. p. 45. 



