INTRODUCTION. j 



number of club-joints has occurred, as in the genera Lucanua 

 and Hexarthrius, approach this tyjje of structure, but more 

 tyjiical forms show only short finger-like ])roductions of the 

 last three joints, ])rovitling a comparatively small extent of 

 sensory surface and capable of very little movement. 



In the FiouLlN-is the three joints are extremely short, almost, 

 if not quite, immovable and (juite Jiard and smooth externally, 

 the sensory surface being confined to their extremities alone. 



The eyes, M^hich are j^laced immediately behind the antennae, 

 are very finely faceted, not very large and with the part visible 

 from above smaller than that on the lower surface of tlie head. 

 Each eye is almost always more or less divided into upj)er and 

 lower ])ortions by a projection of the head in front (called the 

 eantlius), wliich is often more prominent in the female than in 

 the male, so that, together with the mandibles, a triangular- 

 shaped head may be produced in the former sex. The division 

 of the e^'e may be scarcely apparent, as in the genus 

 Cydommatxis ; it may be nearly complete, as in Dorcus 

 cylindricus and rugosus ; or, as in the genera Calcodes and 

 Mgiis, the canthus may actually meet and unite with the 

 hinder part of the head, thus completely bisecting the eye. 



Li females the head is generally short, so that the eyes are 

 not far from the front margin of the pronotum. This is also 

 the case with the males of some species but in many others 

 the head is lengthened beliind and a considerable interval 

 sei)arates ej^es and thorax in this sex. This neck portion of the 

 head is sometimes narrowed and sometimes a little swollen on 

 each side. Sometimes a rather strong projection occurs on 

 each side behind the eye, as in many species of Calcodes, in 

 Dorcus ivimherleyi and oweni, in Jilgus acaminatus, Gnaphaloryx 

 opacus and in particular species of other genera. This 

 peculiar feature, the significance of which is unknown, is 

 usually confined to the male but in Dorcus oweni it is found 

 in both sexes. 



The moutli, although not always, generally shows very 

 considerable differences in the two sexes. The mandibles are 

 always extruded and those of the female are strong biting 

 organs, sharp at the tips, with interlocking projections of the 

 inner edges, which are not the same on the two sides. Between 

 the bases of the two mandibles is a cljqieal process, wliich in 

 this sex is small and generally more or less semicircular. The 

 mandibles of the male rarely if ever show the same fitness for 

 biting as those of the female and are generally quite incapable 

 of any such use, the pressure that can be exerted at the tips 

 being, of course, in inverse proportion to their length. There 

 may be interlockmg teeth near the base or studding the imier 

 edge and then, as in the female, these will not be symmetrically 

 placed ; but this condition is scarcely ever found except in 

 dwarfed males, in which it probably represents the persistence 



