IDEA OK A GENUS. 



593 



never doubtful of the characters requisite to the formation of a genus. 

 Fabricius could not have made a better choice for the determination of 

 genera than of characters deduced from the oral organs and the antennae, 

 ns these organs are of the greatest importance to the existence of the 

 insect, both for procuring its nutriment and in its economy. Their 

 structure is regulated by the former, and they instruct us upon the 

 latter. If, indeed, much may be said against this selection, from the 

 difficulty of their investigation and observation, yet it affords no suffi- 

 cient ground entirely to reject them. Industry and patience overcome 

 much, and the excellent labours of many modern entomologists, for 

 instance, of Savigny, prove that a new era in the history of entomology 

 may be dated from his comparative representation of the oral organs, 

 and especially from his inquiries into the mouth of the Lepidoptera *. 



When such an important point is discovered the definition of the genus 

 is no longer difficult ; it is only necessary to inspect, if the other parts 

 of the body present the same differences as the organs of the mouth ; if 

 this be the case the genus is natural, if not it is artificial and super- 

 fluous. This is likewise the case in the introduction of the neuration 

 of the wing for the determination of genera. In many families the 

 divarication is in such close connexion with the structure of the entire 

 body that a mere view of the wing suffices to show us the difference of 

 genera ; but this is often not the case, and to separate the genus R/iam- 

 phomyia, Meig., from Empis, because it has one nervure less at the 

 apex of the wing, is very artificial, and cannot consist with the prin- 

 ciples of a natural system. These differences can only be used to 

 characterise the divisions within the boundaries of a genus, and thus 

 to facilitate the discovery of a species among a multitude, as Meigen 

 himself has done in the genus Limnobia ; but the divarication in the 

 neuration of the wing cannot be raised to the character of a true genus. 

 But let all entomologists who occupy themselves with the formation of 

 new genera remember the dogma of Linnaeus, " It is not the cha- 

 racter which forms the genus, but the genus, constructed by nature, 

 brings forth the character." 



330. 



Little that is universally applicable can be said upon the value of cer- 

 tain organs for the determination of genera, for even the oral organs are 



* See his M^moiressur les Animaux sans Vertebres. Paris. 1816. 8vo., with figures, 

 vol. i. 



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