18 LUCANID^ AND PASSALID^. 



exactly similar transition can be studied in D. tityus, D. 

 curvidens and other abundant forms. When the two sexes 

 show a different coloration small males may assume the female 

 pattern. For instance, the male Dorcus occipitalis is pale 

 yellow and dull, with a very small black spot in the middle 

 of the thorax ; its female is shining and has a large black 

 spot and a black sutural stripe. Small males may not only 

 be without the structural features distinctive of their sex 

 but may also acquire the glossy surface, the large black spot 

 and black stripe of the other sex. 



This gradual transition from one phase to another, according 

 to the size of the specimens, is the simplest form of male 

 polymorphism occurring in the Lucanid^. The occurrence 

 of two or more j)hases in fully-developed examples of the 

 same species is less well known. The head and mandibles of 

 the males of a Si3ecies may develop differently in different 

 parts of the area of distribution of that species, females and 

 small males being alike throughout the area, while large males 

 present a different aspect in different regions. For instance, 

 in Dorcus foveatus, Plate XV, figs. 2-7 — common in the Hima- 

 layas and Assam— small males (figs. 3, 4) have the mandibles 

 finely toothed along the inner edge. In larger specimens, 

 fig. 5, the edges are smooth in the middle and the teeth are 

 restricted to the base and extremity. In still larger examples 

 some of the basal teeth disappear but two of them persist 

 and become larger, fig. 7. In Assam full-sized males, fig. 6, 

 have only a single large tooth remaining upon the basal half 

 of the mandible, but in the Darjeeling district corresponding 

 examples, fig. 7, have two teeth in this part. This phase was 

 supposed to constitute a distinct species and given the name 

 poidtoni. A similar bifurcation occurs in D. tityus, another 

 Indian species of which the large males have two forms 

 differing in the toothing of the mandibles ; the later-described 

 phase was given the name tethys, in the belief that it was 

 specifically distinct. The most striking example of this kind, 

 is that oi Dorcvs giraffa (Plate XIV, figs. 1,2). The smallest 

 males of this very widely distributed species have narrow, 

 gently curved mandibles of quite sim2)le form. At a more 

 advanced stage the jaws are exceedingly long and there are 

 numerous small sharp teeth scattered along the inner edge. 

 The most highly developed males are of two different types. 

 In certain localities one of the teeth, situated at about two- 

 thirds of the length of the mandible, is much enlarged and 

 the jaw, which is almost straight to that ])oint, is very strongly 

 curved beyond it. This is the form (Plate XIV\ fig. 1) which 

 occurs in Assam, Burma and th(> Malay Peninsula. But in 

 the Darjeeling district and the United Provinces of India, 

 as well as in Tongking and part of China, such specimens are 



