In a highly interesting article in a previous number of this journal (vol. iii, p. 343) J. Dewitz discussed “The bearing of physiology on economic entomology,” and gave in this connection, amongst other things, an account of the various kinds of tropisms and their use, besides which he also pointed out the necessity for studying these for the purpose of discovering weapons for fighting noxious insects. It strikes me, however, as if the importance of chemotropism had not been emphasised in this survey as in my opinion it ought to have been, and the purpose of these modest lines is partly to draw attention to two important researches in this branch of science, recently carried out independently of each other, partly to point out that with the aid of chemotropism we shall in all probability be able to discover new weapons for the fight against noxious insects.