OTHER NATURAL DIVISIONS. 2 63 



These distinctions have long ago been introduced into 

 our systems ; and every practical naturalist, who has 

 made a special study of any class of the animal kingdom, 

 must have been impressed with the propriety of acknow- 

 ledging a large number of subdivisions to express all the 

 various degrees of affinity of the different members of any 

 higher natural group. Now, while I maintain that the 

 branches, the classes, the orders, the families, the genera, 

 and the species are groups established in nature respec- 

 tively upon different categories, and while I feel prepared 

 to trace the natural limits of these groups by the cha- 

 racteristic features upon which they are founded, I must 

 confess at the same time that I have not yet been able 

 to discover the principle which obtains in the limitation 

 of their respective subdivisions. 1 All I can say is, that 

 all the different categories considered above, upon which 

 branches, classes, orders, families, genera, and species are 

 founded, have then- degrees, and upon these degrees sub- 

 classes, sub-orders, sub-families, and sub-genera have been 

 established. For the present, these subdivisions must be 

 left to arbitrary estimations ; and we shall have to deal 

 with them as well as we can, so long as the principles 

 which regulate these degrees in the different kinds of 

 groups are not ascertained. I hope, nevertheless, that 

 such arbitrary estimations are for ever removed from our 

 science, as far as the categories themselves are concerned. - 



Thus far, inequality of weight seems to be the standard 

 of the internal valuation of each kind of group ; and this 

 inequality extends to all groups, for even within the 

 branches there are some classes more closely related among 



1 Professor James D. Dana has Sc. and Arts, 1858, vol. 25, p. 333. 



thrown out some valuable suggestions See also WEIA T LAND (D.), On Series 



upon this point in his review of my in the Animal Kingdom, Proc. Brit, 



"Contributions." See Amcr. Jourii. Nat. Hist. Soc., vol. vi, p. 112. 



