248 Ge7ietical Studies in Moths 



absolutely immovable. In this instance I mixed the last domesticated 

 brood with a random lot from the birchwood, and having shown him a 

 wild and similarly chance lot of alderwood insects I submitted the 

 mixture to a competent lepidopterist for separation. This he did most 

 efficiently, not a single error being made despite the great natural 

 convergence in facies of some individuals in the two races. 



It is worthy of note now, that all friends to whom I have sent ova 

 from various autumnata stations knovvn to me always give it as their 

 weighed opinion that any of the darker races prove the easier to rear ; 

 the birch feeding insect proving especially tricky in its behaviour. This 

 coincides exactly with my own experience with the same insects and 

 with my difficulties with larvae from pale Irish and Scotch birch females. 

 In fact, although it is morally certain that I have bred more of these 

 insects than any other worker, out of batches of ova from at least two 

 dozen Irish females I have never reared a single imago. 



To turn now to experiments with 0. dilutata ; ova from the very 

 white strain attached to the Lonsdale oak island, from Easby Wood 

 melanic females, from pale Irish females and from strigated females 

 taken to the west of Middlesbrough were brought into Middlesbrough. 

 The ova hatched in due course, and the larvae were reared there on 

 food obtained just outside the borough boundary. This was continued 

 for three seasons. In each and every case the insects bred true to their 

 own type and showed the same range of fluctuating variation as it did. 



Finally I obtained ova of 0. christyi, the smaller subspecies of 

 0. dilutata, from Ireland and reared them at Middlesbrough with 

 dilutata and our own form of christyi, which is grey and less silvery in 

 tone. Two years' rearing under the same conditions induced not the 

 faintest trace of convergence ; nor was one expected, for Nature conducts 

 parallel experiments in the two localities known to me which produce 

 both dilutata and christyi, one near Seamer in Cleveland and the other 

 in Durham ; in the former christyi is light grey and dilutata melanic, in 

 the latter christyi is of the very pale type and dilutata of the medium 

 grey tone, and they have always continued so as long as I have known 

 them. 



These observations demonstrate conclusively (1) that the differences 

 between christyi and dilutata are germinal ; (2) that their physiological 

 reactions toward the agent inducing melanism, whatever it may be, are 

 quite different. 



