174 NATURAL HISTORY. 



another in external appearance, and are adapted to entirely 

 different modes of life. It is in the separation of the 

 merely physiological or adaptive characters of an animal 

 from its really essential morphological characters that a 

 great part of the work of the scientific zoologist consists ; 

 and it is also upon characters of the latter class that all 

 modern systems of classification of the animal kingdom 

 are based. 



To return, however, to Swainson and to the circular 

 classification. To some extent, Swainson undoubtedly 

 recognised the underlying distinction between these two 

 kinds of likenesses among animals. He also recognised 

 that all classifications which are based upon likenesses of 

 analogy are necessarily ' artificial/ and that the basis of a 

 ' natural ' classification can only be found in the ' affinities ' 

 or homological likenesses between animals, since these 

 alone are indicative of true relationships. It is singular 

 that, starting with comparatively clear ideas as to what 

 points were of really taxonomic value, Swainson should 

 have given his adhesion to one of the most fantastic and 

 unnatural systems of zoological arrangement which have 

 ever been promulgated. For our present purpose, it is 

 enough to give a mere outline of this system, which 

 Swainson laid down in the following propositions : 



(i) The entire series of animals is a continuous one, 

 forming a circle ; so that, * commencing at any one given 

 point, and thence tracing all the modifications of struc- 

 ture, we shall be imperceptibly led, after passing through 

 numerous forms, again to the point from which we 

 started.' In accordance with this proposition, Swainson 

 divided the entire animal kingdom into five great groups, 



