J. W. H. Harrison 247 



what is experienced in Zonosoma orhicularia, seems most emphatically 

 not to injure the race. 



The reciprocal experiment of attempting to feed larvae obtained 

 from birch-fed autumnata females on heather was carried out in the 

 North Durham area with negative results as far as it went. The larvae 

 attained the fifth instar and in that, as well as in the preceding four, 

 they could not be distinguished from autumnata treated in the usual 

 fashion. Owing probably to the difficulty of keeping Calluna fresh, and 

 the consequent necessity of supplying them occasionally with stale food, 

 they dwindled and died ; not a single pupa was obtained. 



Similar transplantation experiments were made in the case of the 

 feebly marked pinewood race of 0. autumnata. Ova from a mixed 

 selection of wild females from Wilton Wood were brought down to 

 Middlesbrough, where instead of 800 feet, the elevation above sea level 

 is only 30 feet. When they hatched the young caterpillars were offered 

 birch instead of their own larch or pine ; without any hesitation they 

 took it and were successfully reared. As a result imagines were obtained 

 which in every characteristic marking of the race were indistinguishable 

 from those captured in the pinewood ; and this resemblance extended 

 to the period of emergence of the imago which, against all probability, 

 happened towards the end of September, just as did that of its wild 

 relatives. But one difference was recognised ; the imagines averaged a 

 millimetre and a half larger than the wild specimens and now possess 

 a mean size equal to that of the birch-frequenting race. The experiment 

 was continued for three more years but no further change was per- 

 ceptible. Except in size — a character in which they always agreed with 

 the birchwood broods reared alongside of them — the evidence they 

 have to offer is precisely that of 0. filigrammaria, i.e. that the racial 

 characters are germinally fixed ; the size is ontogenetic in this instance. 



Portions of four broods taken wild in the same pinewood were 

 removed to the Team Valley, North Durham, where they were submitted 

 to a hawthorn diet and were kept going for two years ; the results were 

 of the same order as those obtained in the last experiment. An increase 

 of size but a retention of other characters, including those of habit, was 

 exhibited. Clearly the increase in size depends on a removal from the 

 less nutritious pine and larch to the more favourable birch or hawthorn. 



In a further experiment ova from the Lonsdale alderwood (elevation 

 850 feet) were allowed to winter naturally in Middlesbrough and then 

 reared (for three generations) under the same conditions as those used 

 in the case of the pinewood race ; again the racial characters were 



