PREFACE. l\ 



not in birds only, but in the whole series of the verte- 

 brata, for indicating the order of arrangement, or as af- 

 fording a centre of affinities, because their variations 

 are more perceptible. Under this head, however, is to 

 be included the whole series of parts from the bill to 

 the extremity of the rectum. 



All arrangements of birds hitherto published, whe- 

 ther professing to be derived from the consideration of 

 the aggregate of the organization or not, are merely 

 artificial, inasmuch as, in their details, reference is had 

 only to one or a few sets of organs. In all systems, 

 the consideration of the bill is the great principle of ar- 

 rangement, and in that respect the system of Cuvier is 

 just as artificial as that of Linnseus. 



Considering the organs or parts according to their 

 relative importance, we might dispose birds^in a linear 

 series ; which would answer all the purposes of an ar- 

 rangement, provided the other affinities were pointed 

 out by description. In the linear series, of every three 

 species the central ought in some essential respect to be 

 most neai'ly allied to those next it. The same remark 

 applies to genera and orders. According to these pre- 

 mises, the linear distribution ought to be circular. We 

 may commence at any point, that is, with any particu- 

 lar species of bird, and add to that species, on either 

 side, until the order is completed. 



Were such an arrangement founded upon the consi- 

 deration of a single organ, there could be no variation, 



