24 LFCA'NTDiE AXD PA$SALID^. 



calliper-Dke, and a gradual transition can bo followed from 

 very small males in which the form is identical with that of 

 the female. 



A related sjjecies living in Southern India, Friotyrannus 

 niordax, is of particular interest. The female has scissor-like 

 jaws, the edges of which bear fine shar]) saw-teeth. In small 

 males the form is the same and increasing size brings little 

 change, except that the proportionate length of the mandibles 

 become slightly greater. In the very largest males, however, 

 the mandibles are calliper-shaped and a series of . twenty 

 . specimens of tliis sex in the British Museum is equally divided 

 between the two jihases, without any i)assage from one to 

 the other. (Proc. K. Ent. Soc. (A), xiv. 1931>, p. 113.) 



We find then, amongst the Coleoptera, certain forms, likd 

 those of Psalidognathus, in which the transition from the 

 f(Mnale to the male type of mandible is com])lete ; in others, 

 such as most of the Lucanidje, tlie earliest phase, in which 

 the two sexes have identical mandibles, is wanting ; in yet 

 others, like Lucanus, all the early male stages are absent 

 and the dissimilarity is very great, while in Priofyrannus 

 rnordax, Calcodes a'ratus, Dorcus suturalis and such forms, the 

 penultimate male stages have disappeared and we have two 

 distinct phases in that sex. Since sexual dimorphism has 

 an evident connection with large size, those species in which 

 all the stages still exist seem to indicate descent from a smaller 

 ancestor, both sexes of which were alike, the different male 

 phases recapitulating the stages in its evolution that have 

 accompanied increase in size. The disappearance of some, 

 but not of all, the transitional stages is as yet unexplained, 

 and still more difficult to account for is the, no doubt rare, 

 occurrence of two different stages in a single individual. 

 The latter may perhaps be due to some unknown cause 

 operating during tlie pupal period. 



When we })ass from the consideration of the Li'CANid.e 

 to study the Passaliu^, the change from an extremely poly- 

 morphic family to one of exceptional uniformity is surprising. 

 With only two known exeejjtions the colour of the five hundred 

 described species of Passalid.^: is the same — black. The 

 general form of the body is tlie same tliroughout tlie group, 

 and the legs and antenuie do not vary in ])ro])ortion to the 

 size of the insect to which they belong. Moreovi-r, instead 

 of an extreme inconstancy of form in the individuals of the 

 same sjjccies, we find a lemarkable constancy. AVith certain 

 exceptions, the different s])ecies of Passalid^ consist of 

 individuals luuisually uniform in size. Most remarkable of 

 all, not only are the extravagant developments of the male, 

 so frequent in the Lucanid^, cons})icuously absent in the 

 Passalio.I':, but not a single sjjecies is known in th(> family 



