586 TAXONOMY. 



of haustellate insects, although their oral organs are formed as in all 

 beetles. 



b. Repetition of the same form in different grades, for example, a 

 resemblance between genera of different orders, namely, Tipula and 

 Bittacus, Mantis and Mantispa, &c. 



c. A change of form in individual organs, with a general resemblance 

 in the rest, for instance, clavate antennae of Hellwigia among the 

 Ichneumons, filiform antennae in Antftribus among the Curculios, &c. 



3. Typical affinity. It will be found that in general all forms and 

 grades of organisation in a natural group stand in a certain degree of 

 resemblance to each other, which relation is considered as the type or 

 characteristic expression of the group ; where this resemblance is found 

 there is typical affinity. This can present itself as 



The generic type if the species of a genus agree in form, sculpture, 

 and colour. 



The family type, if, for instance, the oral organs, antennae, legs, or 

 the entire form resemble each other in the genera of a family ; and as 



The type of the order if the grades of metamorphoses or the construc- 

 tion of the body evince a certain conformity, as is very evidently the 

 case in the Coleoptera. 



These three kinds of affinity separate and connect at the same time 

 the several groups. Gradational affinity presents the characters of the 

 classes, orders, and higher groups ; typical affinity distinguishes the 

 natural limits of the lower groups. Parallel affinity again connects the 

 several groups together. Thus, upon the similitude and dissimilitude 

 of all the qualities and characters is the natural system founded. 



321. 



It may now be asked what course does the natural system follow in 

 the consecutive arrangement of the groups ? In reply to this, we can 

 scarcely say more than that it arranges the groups according to their 

 affinities, and this series regulated by affinities is the course of the 

 system. Nevertheless we can, proceeding from the essence of the 

 natural system, characterise its course a priori. It is also the task of 

 the natural system to show the developments which a group has passed 

 through from its simple beginning to its extreme perfection. These 

 developments are shown to us by physiology, and therefore every natural 

 system must proceed upon physiological principles. 



