592 



MESSRS. BATESON AND BRINDLEY ON [NoV. 15, 



specimens were few, while the moderately high and moderately low 

 males are common, the two groups heing about equally numerous. 



Measurements of the thoracic horn showed a similar dimorphism ; 

 hut, 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 cephalie 

 horn. Fig. 5 shows the result of grouping the statistics as to the 



Fig. 5. 



Xylotrufcs, gideon, ^ . Table of frequencj' of elytra of various lengths. 

 Ordinates show number of cases ; abscissa show lengths of elytra in cm. 



frequency of the various lengths of elytra, and it is hence clear that 

 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 



