2 LUCANID^ AND PASSALID^. 



jieculiar. The mesotliorax is Icngtlioned in such a way as to 

 form a waist such as few other beetles possess. Tlie mesono- 

 tum does not ])rojcct between the elytra, and the bases of these 

 do not, as visual, fit closely against the pronotum. As a 

 consequence of the elongated mesothorax the second pair of 

 legs is capable of swinging forward into a position close to 

 the axis of the body, impossible to most other beetles. The 

 organs of the mouth are also entirely different in the two 

 families. Those of the Passalid^ form a very strong masti- 

 catory apparatus for dealing with woody material, while those 

 of the LuCANiD^ are adapted for juicy or liquid nourishment 

 and of a much more delicate character, their mandibles not 

 being employed for mastication. 



Another great contrast between the two groups is found in 

 the usually very different males and females of Lucanid^ 

 and their always identical form in Passalid^. A charac- 

 teristic of Lamellicornia in general is the tendency for 

 the two sexes to show considerable differences in form and 

 colouring. The most striking manifestation of this is in the 

 appearance of horns, either peculiar to the males or reaching 

 an exaggerated development in that sex. These horns are 

 either outgrowths of the head or thorax or greatly elongated 

 mandibles. The most remarkable examples of the former 

 type are found in the Dynastin^ and Coprin^, already 

 dealt with in former volumes of this series, and of the latter 

 type the most striking examples occur in the Lucanid^. 

 A few cases of this type have been described and figured in 

 the volume on Rutelin^ {Didrepanephorus, Dicaulocephalus, 

 etc.), and a similar enlargement of the mandibles of the males 

 is met with in particular instances in many families (Ceram- 

 BYCiD^, Brenthid^, Histerid^, etc). But the Lucanid.^ 

 are not only the best examples amongst insects of the enlarge- 

 ment of the male mandible — they are probably unique in 

 exhibiting a high degree of sexual dimorpliism in the great 

 majority of the species. In other instances it is observable 

 tliat these differences between male and female are of very 

 irregular occurrence. They may be found in a single species, 

 in several or in many, but closely related forms are almost 

 invariably found in which they are absent. Usually they arc 

 found in the largest forms of a group and smaller closely related 

 forms are without them. In the Lucantdje also they reach 

 their highest development in large species and are absent in 

 certain small forms, but those in which the two sexes are 

 actually alike are so few as to be comparatively unimportant. 



The PASSALiuiE, on the contrary, are conspicuous amongst 

 the Lamellicornia for the complete absence of external dif- 

 ferences between male and female. Living in similar conditions 

 and, like the LucANiDi^:, feeding in the larval stage in and 



