INTRODUCTION. 39 



its hinder limit, as in Dorcus antseus, etc. Accordingly there 

 may be two lateral spines or angles, as in D. elegans and 

 westwoodi, or, when there is a single lateral angle, this may 

 have originated in either of the two ways. 



The mesothorax nearly always forms a small scutellum 

 between the elytra at their bases and this is usually very short, 

 obtusely angled or semicircular. Jn the Fioulin^, however, 

 the scutellum is very narrow and acutely angled, and in 

 certain species of Figulns it is al^sent altogether. 



The elytra completely cover the abdomen. They may be 

 extremely glossy upon the back but the sides are often 

 rougher and less shining than the dorsal part. Usually there 

 is a gradual transition from rough to smooth surface but 

 sometimes a sharj) dividing line sej)aiates strongly contrasted 

 inner and outer halves, as in Dorcus bimjmitiis and other 

 species. The puncturation of the elytra is evenly distributed, 

 without linear arrangement, and although dee}) longitudinal 

 grooves occur uj)()n the surface in some genera and in the 

 females of certain species such as Dorcus reichei, serial 

 puncturation of the type common in other groups of beetles, 

 probably representing the ancient wing- venation, is usually 

 absent in Lucanid^. With certain exceptions the shoulders 

 of the elytra are square and generally sharj)ly angular. The 

 wings do not diflFer in any important respect from those of 

 other Lamellicornia. The abdomen presents tive cliitinous 

 sternites on the lower surface and, except in a greater or less 

 density of puncturation, these undergo exceedingly little 

 change of form. Although this is a part of the body that in 

 other LamclUcorn groups is especially liable to show sexual 

 differences, in the Lucanid.^ these are almost entirely absent. 



The genital organs of the male present certain pecidiarities. 

 They consist essentially of an outer tube (tegmen) terminating 

 in two lateral lobes, through which passes an inner tube, also 

 bilobed at the end. To the membranous sac contained in tliis 

 is attached a very long flexible Hlament (the flagcllum), the 

 extremity of which assumes ditfcrcnt forms. These structures 

 are not very hard and tlicir relative positions vary. There is 

 a tendency at the present time to regard the genitalia of male 

 insects as free from the variability which affects other parts of 

 the body and, where very well differentiated species are 

 found, considerable constancy is, no doubt, to be found in 

 these structures also. But in wide-ranging forms, examples of 

 which from adjoining areas are indistinguishable, while those 

 from regions far apart show local variations, \ariation can be 

 traced in the genitalia of the same kind as in the externa' 

 foatures. Differences fnimd in individual specimens must 

 therefore be regarded with the same caution as is necessary 

 with the so variable external male features of these insects. 



