72 



PROBLEMS OF RELATIVE GROWTH 



Xylotrupes (Bateson and Brindley, 1892) ? I think that we 



can. Let us begin with the clearer-cut case of Forficula, in 



which there is a definite dimorphism of the male forceps, but 



no dimorphism of female forceps, or of the body-size of either 



sex. 1 



TABLE V 



Measurements of 1,519 Earwigs collected by Djakonov : ana- 

 lysed in Huxley, 1927B, Table I (see Fig. 40) 



Analysis of Djakonov's results (Huxley, 1927B) has shown 

 that when the data are tabulated by body-size, the mean 



1 Recently Kuhl (1928) has attempted to show that the dimorphism 

 of the forceps of male earwigs is apparent only, due to unconscious 

 selection of largest and smallest specimens in collecting. This, how- 

 ever, does not account for the monomorphism of male body-size or 

 of female forceps ; and in any case is quite unable to account for the 

 degree of dimorphism found by Bateson and Brindley, Djakonov (1925), 

 etc. If apparent dimorphism is so easily produced by such means, 

 existing collections should demonstrate it for large numbers of species ; 

 instead it is quite exceptional. 



It would appear that the absence of, or slight tendency to, bimodality 

 shown in Kuhl's material (his pp. 362-3) is to be accounted for by the 

 almost total absence of ' high ' forms in his material, which again is 

 to be correlated with low body-size. The maximum forceps-lengths 

 in his four samples are 6-5, 6-5, 7-5 and 8-o mm. respectively. As 

 my figures show, the ' high ' mode only occurs at 7-5 to 8-o mm. In 

 Djakonov's material the maximum forceps-length is 10 mm., and 

 Brindley (referred to on my p. 313) records a maximum of 12-25 mm. ! 



