58S 



MESSRS. BATESON AND BRINDLEY ON [NoV. 15, 



this, it is to be remembered tbat in most localities the high male 

 is either unknown or very scarce, and it cannot be doubted that in 

 these places the low males are really mature. Lastly, we know by 

 the analogous case of horned beetles that high males coexist with 

 low males, both being in this case of course mature. We think, 

 therefore, that we are justified in conjidering that the 583 males 

 available for measurement were all adult. 



These specimens were laid out on squared millimetre paper 

 covered witli gum, and while the gum was still wet the posterior end 

 of the forceps was brought up to one of the lines, and the length of 

 the forceps was read to the nearest half millimetre, which is well 

 within the limit of error. The results are set out in the accompany- 

 ing curve (fig. 2), in which the figures on tlie ordinates denote 



Fig. 2. 



Curve showing frequency of occurrence of forceps of various lengths iu male 

 Earwigs {F. auricidaria). 



Ordinates give numbers of individuals; abscissae give length of forceps iu mm. 



numbers of individuals, those on the abscissae denoting millimetres. 

 The smallest length of forceps was 2*5 mm., and the greatest 9 mm. 

 As the curve shows, the greatest frequency is grouped about 3'5 

 mm. and 7 mm. respectively. The mean form, having forceps of 

 moderate length, -1-6 mm., is comparatively rare. We consider that 

 the number of cases is enough to justify the acceptance of these 

 statistics, and it is unhkely that a greater number of cases would 



