l8o NATURAL HISTORY. 



have the fewest of the characters common to the series, 

 and which therefore necessarily possess many characters 

 common to other groups of animals. Moreover, Swainson 

 considered that every 'aberrant' group exhibited three 

 principal modifications of structure, which constituted 

 the basis of as many minor groups. One of these 

 subordinate sections of the aberrant group was supposed 

 to contain animals adapted for an aquatic life. The 

 animals of a second section were supposed to be adapted 

 for obtaining their food by suction; and a third or 

 'rasorial' section was formed for the reception of types 

 adapted for scratching or for climbing. Thus, as 

 shown in a preceding diagram, the Mammals are the 

 'typical' group of Vertebrates, and the birds are the 

 ' sub-typical ' group ; while the ' aberrant ' group comprises 

 the 'aquatic' section of the fishes, the 'suctorial' 

 group of the Amphibians, and the 'rasorial' group of 

 the reptiles. 



Now starting with this basis admitting, that is, that 

 you could divide a given series of animals into three 

 primary groups, a typical, a sub-typical, and an aberrant 

 group, and admitting further that the last contains three 

 minor groups, one aquatic, one suctorial, and one 

 rasorial the fundamental proposition of the circular 

 classification is, that every series of animals can be 

 similarly divided, and that each quinary system, however 

 small, must represent each and every other system. If 

 it does not do so, it is, ex hypothesi, not a natural group. 

 By way of exemplifying this proposition, we may present 

 here the tabular view which Swainson gives of what he 

 regards as the 'beautifully simple and harmonious' 



