234 ESSAY ON CLASSIFICATION. 



their structure. Families stand higher or lower, according 

 as the peculiarities of their form are determined by modi- 

 fications of more or less important systems of organs. 

 Genera stand higher or lower, as the structural pecu- 

 liarities of the parts constituting the generic character- 

 istics exhibit a higher or lower grade of development. 

 Species, lastly, stand one above the other in the same 

 genus, according to the character of their relations to 

 the surrounding world, or that of their representatives 

 to one another. These remarks must make it plain that 

 the respective rank of groups of the same kind among 

 themselves must be determined by the superior or inferior 

 grade of those features upon which they are themselves 

 founded ; while orders alone are strictly defined by the 

 natural degrees of structural complications exhibited 

 within the limits of the classes. 



As to the question, whether orders constitute neces- 

 sarily one simple series in their respective classes, I would 

 say that this must depend upon the character of the class 

 itself, or the manner in which the plan of the type is car- 

 ried out within the limits of the class. If the class is ho- 

 mogeneous, that is, if it is not primarily subdivided into 

 sub- classes, the orders will, of course, form a single series ; 

 but if some of its organic systems are developed in a dif- 

 ferent way from the others, there may be one or several 

 parallel series, each subdivided into graduated orders. 

 This can, of course, only be determined by a much more 

 minute study of the characteristics of classes than has 

 been yet made, and mere guesses at such an internal 

 arrangement of the classes into series as those proposed 

 by Kaup or Fitzinger can only be considered as the first 

 attempts towards an estimation of the relative value of 

 the intermediate divisions which may exist between the 

 classes and their orders. 



