120 AMERICAN JOURNAL 



W, Swainson has the merit of introducing a truly scientific 

 method of determining the values and relative ranks of the vari- 

 ous zoological divisions, although the manner in which he fol- 

 lowed his own rules proved erroneous in most instances, not be- 

 ing based sufficiently on anatomical inquiries, at that time in 

 their first infancy. The following rules of Swainson appear to 

 me to be the most important. 



" The true rank of a natural group can only be detected by 

 analysis and analogy ; and the more extensively these enquiries 

 are carried into the neighboring groups the more likely are we 

 to understand its true rank."* 



" The verifications of a natural group are three, (Sw. ib. p. 

 287.) ^ ^ '^ ^ 



I. The circular series of its contents. 



II. The parallel relation of its parts to other groups. 



III. The symbolical representation of the primary types of 

 nature. 



The first rule may be considered imaginary and entirely in 

 opposition to the second. 



The arrangement according to analogy in parallel series was 

 first used by Oken and Agard, and may be considered the only 

 true manner of natural arrangement. MacLeay considered the 

 series as assuming a circle, but Swainson has explained it more 

 fully. 



How well Linnef understood the application of this arrange- 

 ment to show the difference between affinity and analogy, is 

 proved by his arrangement of the faculties of the human mind 

 and the systematic terms of rank, but he did not consider it 

 proper for the arbitrary system he was compelled to use for want 

 of the natural system. 



The third verification, the theory of representation, is con- 

 sidered by Swainson the only certain test of a natural group. 

 " Every perfect group has its own typical and aberrant forms ; 

 and these are represented by the typical and aberrant forms in 

 another perfect group. In tracing the analogy between two 

 series of animals, we can never compare a typical group in one 

 circle with an aberrant group in another." The latter sentence 

 is exceedingly important and indispensable to any comparison, 

 but frequently neglected. 



* Swainson on classification, p. 169. 



t Syst. naturae ed. xii. p. 11, 13, 17. Amoenitates acaderaicae, vii. p. 

 326. Philos. botanica, ^ 155. 



