388 HISTORY OF ZOOLOGY. 



men can neither overlook the general physiological 

 features of animals, nor avoid being swayed by 

 them in their judgments of the affinities of different 

 species. Thus the classifications of zoology tended 

 more and more to a union with comparative anatomy, 

 as the science was more and more improved 18 . But 

 comparative anatomy belongs to the subject of the 

 next Book ; and anything it may be proper to say 

 respecting its influence upon zoological arrange- 

 ments, will properly find a place there. 



It will appear, and indeed it hardly requires to 

 be proved, that those steps in systematic zoology 

 which are due to the light thrown upon the subject 

 by physiology, are the result of a long series of 

 labours by various naturalists, and have been, like 

 other advances in science, led to and produced by 

 the general progress of such knowledge. We can 

 hardly expect that the classificatory sciences can 

 undergo any material improvement which is not of 

 this kind. Very recently, however, some authors 

 have attempted to introduce into these sciences 

 certain principles which do not, at first sight, ap- 

 pear as a continuation and extension of the previous 

 researches of comparative anatomists. I speak, in 

 particular, of the doctrines of a Circular Progres- 

 sion in the series of affinity ; of a Quinary Division 

 of such circular groups; and of a relation of Ana- 

 logy between the members of such groups, entirely 

 distinct from the relation of Affinity. 



12 Cuvier, Leg. d'Anat Comp. vol. i. p. 17- 



