1 78 NATURAL HISTORY. 



fives, this could only be because we knew too little 

 about them to make them do so. Thus, as shown 

 above, there were five sub-kingdoms, or primary divisions, 

 of the animal kingdom. Each sub-kingdom was similarly 

 divisible into five classes, as shown above in the case 

 of the Vertebrates (in which there really are five classes). 

 Each class fell to be divided into five orders, each order 

 into five families, and so on. 



As just mentioned, however, Swainson did not accept 

 this quinary arrangement without some modification. 

 He thought that three was the governing number; but 

 then he supposed that one group could always be 

 divided into three smaller circles. In any three groups 

 forming a closed system one group is what he called 

 'typical,' a second is ' sub-typical,' and the third is 

 'aberrant'; but the aberrant group itself forms a closed 

 system of three smaller circles, thus : 



Aberrant Group 



