IN the abstract of Prof. Moseley's interesting lecture on “The Fauna of the Seashore,” published in the current number of NATURE (p. 212) several agents are referred to as competent to call into play the tendencies to vary which are embodied in each species. These, whether suggested by Prof. Loven or the author of the lecture, include—light and shade, temperature, currents, food, enemies, favourable condition of water for respiration, and the variation of conditions produced by tides. I venture to think that one very important factor in the variation of the marine fauna, if not the most important, has been left out of the list: I refer to marine waves.