4 INTRODUCTION. 



be sure that our conclusions agree with what may be 

 observed in nature. 



It appears to me, however, as a principle unobjectionable 

 in itself, that the adoption of any organ, not immediately 

 connected with the sexual difference, for purposes of ge- 

 neric arrangement, ought to be in an inverse proportion to 

 the difference of that organ in the sexes. So that when 

 we find the form of the mandibles, for instance, to differ in 

 the sexes of the genus Lucanus, we ought to choose some 

 other test by which we may distribute these insects into 

 natural groups. 



I shall perhaps be more clearly understood from the 

 inspection of the following table, in which I have attempted 

 to class, according to their degree of variation as to form 

 or number, first in the sexes, and secondly in the species, 

 all the various organs which have been the keystones of 

 different systems. This table, however, is to be considered 

 with reference to the Coleopterous insects only. 



Capitis Thoracisque 

 Co ran a vel Gibbere; 



Ala; 



Tarsorum Articuti . . 



Pedum Ungues 



Scutellum distinctum 

 Sternum productum 



Palpi 



Antenna; 



Pedes 



Mandibular 



Mentum 



Oculi 



Maxillae 



:l 



In the Sexes. 



As to 

 Number. 



variable 



variable 



variable 



invariable? 



invariable 



invariable 



invariable 



invariable 



invariable 



invariable 



invariable 



invariable 



invariable 



As to Form 



variable 



variable 

 invariable? 

 invariable 

 invariable 

 variable? 

 variable 

 variable 

 variable 

 invariable? 

 invariable 

 invariable 



In the Species. 



As to 

 Number. 



variable 



variable 



variable 



variable 



variable 



variable 



variable 



invariable 



invariable 



invariable 



invariable 



invariable 



invariable 



As to Form. 



variable 



variable 

 variable 

 variable 

 variable 

 variable 

 variable 

 variable 

 variable 

 variable 

 variable 

 variable 

 variable 



a It is possible that the form of the mentum may be found to differ ia 

 the sexes of some of the Linnsan Lucani ■ 



• 



