OCR Text |
Show 592 MESSRS. BATESON AND BRINDLEY ON [Nov. 15, specimens were few, while the moderately high and moderately low males are common, the two groups being about equally numerous. Measurements of the thoracic horn showed a similar dimorphism ; but, for the reason that it is not possible to measure this horn apart from the thorax, these measurements are not so satisfactory. The length of the elytra was also measured, and it may perhaps be taken as a measure of the body-length. For various reasons it is hard to obtain any more satisfactory measurement of the body-length. Such a measurement must either include the variable horns or else must depend on the degree of flexion of head or thorax. The result of the measurement of the elytra is perhaps unexpected in view of the knowledge that there is dimorphism in respect of the cephalic horn. Fig. 5 shows the result of grouping the statistics as to the Fig. 5. Xylotrupes yideon, 3. Table of frequency of elytra of various lengths. Ordinates show number of cases ; abscissae show lengths of elytra in cm. frequency of the various lengths of elytra, and it is hence clear the mean form is the commonest, just as it is in the case of the stature of a given human community. Though dimorphic in respect of the length of the horns, these males are thus monomorphic as regards the elytra. There is of course nothing really contrary to |