78 PROBLEMS OF RELATIVE GROWTH 



largest females only 25 mm. As the mandibles of the male 

 are highly heterogonic (ranging up to 88 per cent, of body- 

 length), the disparity in total size is even greater. This differ- 

 ence would appear only to be obtained on the basis of possible 

 extra moults in the male. In this form the frequency curve 

 for all mandibles is again multimodal, with two main and one 

 or more subsidiary modes. But the multimodality is not so 

 well defined when curves for separate body-size classes are 

 plotted. There is also a slight tendency to multimodality or 

 at least irregularity in the male body-length frequency curve. 

 No multimodality is apparent in the Lucanus curves. Thus 

 here again the insect with the presumption of a facultative 

 extra moult is characterized by multimodality of heterogonic 

 organ. 



A case of male dimorphism in the Acarine mite Analges 

 accentorinus which would appear to be due to similar causes 

 has been described by Jucci (1924). Here the large adult 

 males are characterized by a great hypertrophy of the third 

 pair of limbs. There further exist small but also adult males 

 whose third limbs are almost identical with those of the female. 

 From the scale drawings given by Jucci, we can say that the 

 size-difference between the two forms is very close to what 

 we would expect (on the supposition that bulk is approxim- 

 ately doubled at each instar) if the larger had had one more 

 instar in its development than the smaller (Fig. 43). 



In addition, occasional small males are found with slightly 

 enlarged third limbs : these would be specimens in which the 

 onset of heterogony had taken place slightly earlier than 

 usual. The case is thus very similar to the earwig, save that 

 the normal ' low ' type is more like the female than in Forficula. 



Having concluded this survey of special cases, I shall in the 

 next chapter pass to a more detailed analysis of the empirical 

 laws of relative growth in heterogonic organs or regions. 



