1892.] VARIATION IN SECONDARY SEXUAL CHARACTERS. 



591 



in the state of nature, Baron von Hiigel tells us that he has no 

 reliable recollection on this point. 



The habit described above is not confined to X. gideon, for 

 Baron von Hiigel observed it also on one occasion in the case of 

 Chalcosoma atlas, the vrell-known Atlas-beetle. A pair of this 

 species from Java were presented by him to the Cambridge Museum, 

 which were thus found, the female being carried between the horns 

 of the male. In view, therefore, of the fact that the horns of many- 

 species are in various ways disposed as a pair of forceps, it is possible 

 that this may be a habit widely spread ; but that such a function 

 cannot be attributed to all the cases of horns is shown by the fact 

 that in many species the horns do not form a pair of forceps. 



In 342 males of this beetle the cephalic horn was measured with 

 compasses from the angle of the terminal fork to the edge of the ridge 

 into which the horn is proximally and ventrally reflected, just in front 

 of the eyes. The results obtained are tabulated in fig. 4, according 



Mm 



Diagram showing frequency of various lengths of the cephalic horns 



in Xylotrujpes gideon, (^ . 



M, mean case ; M', mean value. Ordinates show number of cases ; abscissse 

 show lengths four times nat. size. The numbers give the lengths in lines. 



to the common system. Each dot represents a case, and the ordin- 

 ates thus give the numbers of cases, while the abscissae show the 

 lengths of the horns ; for clearness these measurements are shown four 

 times the natural size. The shortest cephalic horn was 0*4 cm., 

 while the longest was 2*4 cm. As the diagram shows, in the neigh- 

 bourhood of the mean value (M') for the length of horn the 



40* 



