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Show 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 well-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, Justin front of the eyes. The results obtained are tabulated in fig. 4, according Fig. 4. Diagram showing frequency of various lengths of the cephalic horns in Xylotrupes gideon, 3 • M, mean case; M', mean value. Ordinates show number of cases; abscissas show lengths four times nat. size. The numbers give the lengths in lines. to the common system. Each dot represents a case, and the ordinates 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 neighbourhood of the mean value (M') for the length of horn the |
