278 Genetical Studies m Moths 



case the latter is the correct explanation for seven ova passed from 

 green to pink only to fail to develop in spring. 



Similar attempts to pair 0. autumnata and Gheimatohia brumata 

 proved utterly futile, no ova appearing at all. 



IV. Summary. 



(1) The' genus Oporahia is of Boreal origin and distribution; it 

 comprises within its limits in its British range two species, Oporahia 

 autumnata and 0. dilutata, each possessing a well defined subspecies 

 and numerous local races. 



(2) All of these forms, no matter what their value, display enormous 

 variability, and their variations occur in parallel series. 



(3) All develop melanic and melanochroic races and aberrations. 



(4) It is suggested that the subspecies Oporahia filigrammaria 

 was evolved from 0. autumnata on non-glaciated areas to the west of 

 the British Islands of today ; this event was caused during the Glacial 

 pe,riod by the action, direct and indirect, of changed climatic conditions. 



(5) The genesis of local races, it is further pointed out, is brought 

 about by natural selection limiting the range of variation by the 

 elimination of genetical strains less protected in any given habitat. 



(6) Almost certainly, many of the changes exhibited, both those 

 of racial and those of subspecific value, are true Lamarckian effects. 

 In particular, food instincts in 0. filigrammaria, period of emergence in 

 the pinewood race of 0. autumnata, are only explicable on such a basis. 



(7) The differences in size between the various local races of 

 0. autumnata are shown to be ontogenetic and to depend on the food 

 plant. 



(8) Such characters as mark both subspecies and local races, save 

 that of size, are proved experimentally to be germinally fixed. 



(9) Genetically distinct strains exist within the local races as was 

 demonstrated by experiment. 



(10) It is urged that the currently accepted explanations of 

 melanism, in which the inducing cause is stated to be moisture followed 

 by natural selection directed by the darkened resting places in manu- 

 facturing and rainswept areas, do not adequately account for the 

 phenomenon, the premises for such an argument not having been 

 correctly determined. 



