18.02.] VARIATION IN SECONDARY SEXUAL CHARACTERS. 



.593 



expectation in the fact that a race is dimorphic in respect of one 

 character while in respect of another it is mnnomorphic. 



III. LuCANUS CERVus. (The Stng-beetle.) 



Of this insect we have no quantity of males sufficient to justify 

 a statement that in respect of the development of the mandibles it is 

 monomorphic or dimorphic. It is well known that very striking 

 differences are found between high and low males in this species. 



Males to the number of 1 15 obtained at Woking in 1891 and 1892 

 have been measured. The lengths of the mandibles from the apex 

 to the internal angle between the base and the head were taken with 

 compasses, and the result is exhibited in fig. 6. The fact that thig 



Fix. 6. 



Table of frequency of various lengths of mandible in Lueanus cermcs, (J. 

 Ordinates show number of cases ; abscissae give lengths of mandibles in cm. 



sample is monomorphic is quite clear, for the numbers are plainly 

 grouped round the middlemost value. But in this case there is 

 serious reason to doubt whether the sample examined contains really 

 low males. In our experience of the Earwig's forceps and the 

 Xylotrupes horns, the low males are almost like the females; but in 

 the case of the Stag-beetle the mandible of the lowest male seen 

 was much greater than that of the females. It seems possible that 

 in the Stag-beetle the truly low male is either very rare or does not 

 occur, and that the existing individuals belong to a group answering 

 to those which were found in ^ylotrupes above the middlemost 

 value. There is in fact a possibility that we have in the Stag-beetle 

 a case which is the converse of that of the Earwig. In most places 

 the low male Earwig is to be found, the high male being absent or 



