204 Genetical Studies in Moths 



The imagines emerge in the afternoon and remain during the rest of 

 their first day at the base of the tree boles and amongst the herbage. 

 After the first evening's flight they rest higher up, often enough very 

 conspicuously on tree trunks, but sometimes on smaller twigs and 

 amongst leaves. Both sexes, the female in particular, delight to sit on 

 the smaller twigs with their wings encircling them. 0. filigraniTnaria 

 in some of these respects necessarily differs ; both sexes sit on heather 

 twigs, but if rocks are available they may be seen dotted about them in 

 considerable numbers. In all cases the insects are easily startled or 

 dislodged, the males flying high and far and the females but a short 

 distance ; in fact, not uncommonly the female feigns death and drops 

 amongst the herbage. 



The eggs are laid at the base of buds either on the bud itself, between 

 it and the stem, or under tiny curled pieces of bark where they remain 

 sheltered from all the vicissitudes of winter. 



It was my good fortune to discover all of the forms referred to above 

 in my own immediate neighbourhood and therefore within easy reach 

 for study. I at once commenced to experiment with them, and very 

 early indeed I discovered their interspecific fertility and, in certain cases, 

 that of the hybrids of the F^ generation. These latter observations, 

 coupled with the discovery of the constancy of the several local races 

 evolved from 0. autumnata and 0. dilutata, formed a combination so 

 attractive to a geneticist that I determined to avail myself of the oppor- 

 tunities thus offered and to submit the whole of the phenomena presented 

 to more intense study. In doing so I propounded for solution the 

 following problems : 



(1) Seeing that 0. autumnata and 0. filigra.mmaria are perfectly 

 fertile when crossed, and since the F^ hybrid generation is likewise 

 fertile when paired inter se or when back-crossed with either parent 

 species, is the type of inheritance shown explicable on strictly Mendelian 

 lines ? 



(2) What light do the hybrids between 0. autumnata and 0. dilutata 

 throw on the same problem ? 



(3) Further, since 0. autumnata and 0. filigrammaria differ in 

 mean size in both sexes, what information can be gleaned from their 

 study as to the inheritance of size ? 



(4) How do these same two forms maintain their distinctness even 

 when free to cross through their colonisation of the same or adjacent 

 areas ? 



(5) Do the differences between the various local races, as well as 



