I HAVE recently observed very well marked phenomena, similar to those described by Dr. C. O. Whitman (Quart. Journ. Micro. Science, vol. xxvi. new series, p. 409). I picked up with my fingers a stone from the soft muddy bottom of a shallow, torpid stream. Returning to the same spot a few minutes afterwards, I noticed a number of leeches (apparently Hirudo sp.) swimming near the spot. On the following day, suspecting that they had “smelt” or “tasted” my hand in the water, I first stirred the surface of the mud with a stick, but no leeches appeared; after the water was clear again I “washed my hands” in the water without disturbing the mud, and very soon a number of leeches came up and swam about. The soft mud in which they live is about a foot deep, and although the disturbance of the surface mud with a stick was not sufficient to bring them out, the “smell” or “taste” of my hands seems to have spread down and extended over an area of more than a yard.