16 LucANiD-a: and passalid^. 



brookeanus, in which the mandibles have two different phases, 

 in one meeting closely and in the other widely separated, a 

 very conspicuous clyjieal process aj^pears between them in 

 the latter phase but is quite absent in tlie other. 



The astonishing difference commonly found in the mandibles 

 of the two sexes needs no emphasis but the other organs of 

 the mouth usually differ also. The maxillae in many species 

 have a hooked termination to the lower lobe in the female 

 but not in the male, the palpi are often elongated in the latter 

 and the mentum may differ in shape and sculpture or have a 

 clothing of hair in the male, which is absent in the female. 

 The hook-like backward extension of the mentum in the male 

 Figulus cavicejjs is remarkable, since it occurs in a genus of 

 which the other species have identical males and females. 



The head of the female is commonly shorter, as well as 

 more roughly sculptured, than that of the male, w^liich is 

 usually rather smooth, and, apart from the head, the sculpture 

 of the upper surface is rarely the same in both sexes. The 

 female may be glossy and the male dull, as in Calcodes 

 mratus and Dorcus wimberleyi, or conversely the female may 

 be less smooth than the male, as in the genus Cydommatus. 

 In Dorcus reichei, curvidens and hyperion, the elytra, smooth 

 in the male, are very deeply grooved in the female. The 

 antennae of the male are generally longer than those of the 

 female, but the much greater development of the sensory 

 part of these organs, so conspicuous in many Lamellicorns 

 and other insects, is rarely found in the Lucaxiu^. 



In one rather primitive genus, Sinodendron, aheady men- 

 tioned, which is found in Europe and also in North America, 

 there is no enlargement of the mandibles of the male but instead 

 there is a horn upon the head like that of a rhinoceros in the 

 male but rudimentary in the female. In certain Indian 

 species the female (e. g. in Dorcus nepalensis) has a rudimentary 

 horn in the same position, of which there is no trace in the 

 male. Other females {D. reichei, etc.) have two little eleva- 

 tions at that point and in Dorcus derelictus these become 

 rather sharp processes placed at the hinder edge of a sUght 

 depression. They are unrepresented in the males but, 

 strangely enough, the males of certain other sjiccies of the 

 genus, Dorcus foveatus, etc., have a pair of exactly similar 

 sharp processes, also occupying the liinder edge of a dei)ression 

 and not represented in the females. We must conclude that 

 ancestral forms have existed in which both sexes had such 

 processes upon the head. It has been suggested by Lameere 

 that the Lucantd^ are derived from ancestors with liorns 

 but without exaggerated mandibles and tliat, by a comjiensa- 

 tory ])rocess, a gradual enlargement of the mandibles accom- 

 panied the simultaneous (lisa])pearance of the horns. Darwin, 



