Experiments on the egg-laying instincts of the sawfly, Pontania salicis Christ., and their bearing on the inheritance of acquired characters; with some remarks on a new principle in evolution

In the course of genetical investigations (Harrison, 1920) in the lepidopterous genusOporabia I conceived the idea that the inherited instinct ofOporabia filigrammaria HS. to deposit its eggs on heather (Calluna vulgaris ) was the direct result of long-continued isolation on treeless heather-clad moorlands, involving a compulsory diet of that plant; in other words, I felt that the development of the instinct and its inheritance were Lamarckian effects. To test these views experimentally, by attempting a transference in the food habits of other insects, seemed far from difficult, and search was forthwith made for material easy to manipulate in captivity. No forms appeared more adapted for the purpose than the Geometrid mothsLycia hirtaria Cl. andPhigalia pedaria F., which I had employed in former experiments. However, the technique adopted, at any rate as applied to these insects, proved unsatisfactory and had therefore to be modified. Unexpected difficulties, riot in securing oviposition in a state of semicaptivity but in its taking place in a natural manner on the food plant, were immediately encountered.