| OCR Text |
Show 1892.] 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 monomorphic. III. LUCANUS CERVUS. (The Stag-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 115 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 this Table of frequency of various lengths of mandible in Lucanus cervus, 3- 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 Xylotrupes 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 |
