PREFACE. 9 



Every species is perfect in itself, and forms a centre 

 of affinities. For this reason, the assumption of a spe- 

 cies as typical is arbitrary, and merely supplies an ob- 

 ject with which others may be compared, for the pur- 

 pose of composing a group qualified to form part of an 

 artificial system. Any one species being just as typi- 

 cal as another, many birds may be referred to one or 

 another genus, according to the peculiar views of the 

 person who arranges them. 



It is impossible in a linear series to shew all the re- 

 lations of birds, because the successive juxtaposition of 

 the species disrupts their numerous affinities. Neither, 

 for the same reason, can the affinities of species or ge- 

 nera be pointed out by any series of circles or other 

 figures, arranged on a flat surface, such as that of a 

 sheet of paper. Generic groups, to represent affinities, 

 would require to be suspended in empty space, and 

 specific forms would require to be individually extend- 

 ed in different directions, or to present linear prolon- 

 gations meeting, crossing, or uniting with those of 

 other species. But a generic group has so m.iny affi- 

 nities with other groups, that the disposition of such 

 groups in space according to relation is impossible. 

 Still more complex would be the disposition of species, 

 were it practicable ; wherefore the linear series, that is 

 the arrangement of species one after another, whether 

 the series be straight, curved, circular, or disposed in 

 some other form, is the only practicable one. 



