J. W. H. Harrison 227 



This early leafing in itself may be an active agent in causing ova to 

 hatch early, for eggs laid on larch buds would be exposed to the elevated 

 temperature due to the rapid metabolism of the expanding buds much 

 sooner than those on birch and would therefore hatch earlier. In addi- 

 tion, the superior transpiration of Larix over Betula during winter and 

 spring when both are denuded of leaves may, indirectly, serve to secure 

 the same end. 



This explanation would meet the facts of the case admirably, but 

 the following fact must be emphasised ; to grant its germinal fixation 

 is to adopt the Lamarckian view. In my opinion this is the correct 

 explanation, its fixation being brought about by its score or more years 

 of incidence. Taken to a height of 1000 feet in Northumberland, at 

 sea level in Yorkshire, at 300 feet in Durham, in Kent, London and 

 Ireland, with wonderful uniformity the pinewood ova hatch the earlier, 

 and their imagines develop the sooner — facts that render the evidence 

 of my breeding experiments as to its germinal nature the more 

 emphatic. 



Whether it fits in with one's bias or not, with persistent unanimity 

 every little point connected with the divergence in habit and instinct in 

 these researches points to such features being genuine Lamarckian effects. 



Before leaving the subject of the pinewood insect I must mention 

 that in 1908 I beat several aberrational larvae from Pinus sylvestris 

 which were ornamented with rusty patches approximating the larvae 

 in appearance to the condition of such pine feeding larvae as Ellopia 

 prosapiaria; these have never occurred again, thus any study as to 

 their genetic behaviour is rendered impossible. 



The case of the Lonsdale alderwood race need not detain us long. 

 There the conditions are not fundamentally different from the mean of 

 those of the Eston birch and pine woods. We have the more open 

 nature of the one and its less accumulations of moss and needles, 

 coupled with the presence of owls and night-jars to act as selective 

 agents, in conjunction with the abundant patches of larch and pine 

 tending to preserve by selection the darker individuals, but much less 

 rigorously than in Wilton Wood. Inevitably a progression of the modal 

 condition towards darkness has been displayed, resulting in the produc- 

 tion of a race including strains intermediate in many respects to the 

 other two. But, nevertheless, the period of emergence is not signifi- 

 cantly moved ; the very rapid rise in temperature in the wood during 

 June, July and August owing to its patchy, open nature, aided by the 

 very late leafing (often late May) of the alder, definitely ensures this. 



Joum. of Gen. ix 15 



