Note 29 — LECTURE XXXIII

That this suggestion was not unjustified is evident from a recent contribution by Simroth ('Ueber die Raublungenschnecken,' Naturwissenschaftliche Wochenschrift, December 8 and 15, 1901). In this paper the author, who is an expert as regards the biology of Gastropods, shows that a change of diet may evoke many kinds of changes in the structure of the food-canal, which may indirectly compel changes in the shell. Thus in a small indigenous snail, Daudebardia, the pharynx has grown so enormously in thickness and length in adaptation to the predatory mode of life, that the head and the anterior part of the body can no longer be retracted within the shelter of the shell. For this reason, and also because of the snail's habit of following earthworms into their burrows, the shell has been shunted far back and obliquely downwards. It has at the same time markedly changed in its shape, as may still be verified by comparing the form of the shell in the young stages with that of the adult.