TAXONOMY. 



of the larva ; upon the type upon which the oral organs are formed, whe- 

 ther mandibulate or haustellate ; or upon the fundamental form in the 

 structure of the wings. All these relations, indeed, produce an external 

 resemblance, but these resemblances are the result of physiological 

 divarications. The orders are properly families of greater compass, 

 yet with the distinction that the family characters are founded upon 

 a similarity of form of individual limbs, as the feet, antennae ; whereas 

 the characters of orders are derived from a similarity of form of the 

 body. 



There are likewise other subdivisions between an order and its 

 families, as between a family and its genera, which have been called 

 sub-orders, or tribes. The characters of such groups generally consist 

 in the different form of a certain organ, but which differences, from 

 their wider distribution, admit neither of being applied to family divi- 

 sions nor to generic divisions. Thus the Coleoptera are divided into tribes 

 from the number of their tarsal joints, the Diptera according to the 

 number of the joints of the antennae, the Hymenoptera according to the 

 structure of the sting, &c. Yet such tribes are more artificial than 

 natural, which admits of being demonstrated in the three examples 

 cited; they can merely serve to facilitate finding the families, and are 

 not to be considered as natural groups. 



335. 



The classes, lastly, are the highest groups of animals ; which, like 

 the orders, are founded upon the differences of an otherwise uniform 

 grade of structure, and consequently repose upon the differences of the 

 grades of organisation. An equal structure and form of the organic 

 systems and the thence produced very general conformity of external 

 figure, a similarity of periods of development, and other similar rela- 

 tions are the characters which justify the formation of classes. All 

 insects collectively form one class, in as far as they actually agree with 

 each other in the above characters. 



The objects forming classes consequently neither require to be con- 

 gruent nor equal, nor even externally to resemble each other, as these 

 qualities are deduced from a conformity of external figure, but they must 

 all, physiologically considered, be of equal value ; they must all, to 

 make use of a mathematical illustration, be pure geometrical inconstant 

 magnitudes, and not at the same time likewise algebraical constant 

 magnitudes, both of which are virtually different. 



