Having laid some earth worms upon a plate of zinc, I tried to excite contractions in them, by passing a rod of silver over different parts of their length, till it came in contact with the plate; but for a long time without producing any effect. Application of the metals to a part recently divided seemed to produce as little effect. At length, I perceived one of them dart itself forwards, whenever the silver was passed under its belly near to a part which had been divided and rejoined. On repeating the experiment again, and with more care, I found, (as in the frog,) that when the animal was perfectly lively, and upon its guard, no contraction could in this way be excited; but that when a part had been rendered more sensible by previous disease, recent irritation, &c. or when the worm was taken unawares by hanging it over a probe, and lowering both upon the plate at the same instant; a sudden and involuntary motion seemed to dart through a great part of the worm’s length from the part touched towards the head; a direction contrary to that in which it takes place in other animals. I never could produce the same effect upon leeches. On varying the experiment, a most whimsical, but satisfactory phenomenon presented itself. I had laid a leech upon a crown piece of silver, placed in the middle of a large plate of zinc. The animal moved its mouth over the surface of the silver without expressing the least uneasiness; but having stretched beyond it and touched the zinc plate with its mouth, it instantly recoiled, as if in the most acute pain, and continued thus alternately touching and recoiling from the zinc, till it had the appearance of being quite fatigued. When placed wholly upon the zinc, it seemed perfectly at its ease; but, when at any time its mouth came in contact with the silver lying upon the zinc, the same expression of pain was exhibited as before. With the earth worm, this experiment succeeded still more decisively. The animal sprang from the zinc in writhing convulsions; if, when the worm stretched itself forwards, one of its folds lit upon the zinc, it expressed little uneasiness in comparison of what it shewed when the point of its head touched the zinc. These extraordinary effects were, however, considerably different from those produced by the metals upon the limbs of frogs, and other animals. They had not so much the appearance of involuntary, instantaneous convulsions, as long continued expressions of pain and disgust; such as are produced by applying zinc and silver to the tongue of a child. A strong presumptive proof, in my humble opinion, that these animals are endowed with a most exquisite organ of sense, and, consequently, that they are not, as has been supposed, destitute of a nervous system. Doubtful, therefore, if this influence can ever act upon the muscular fibre, except through the medium of nerves, I shall reserve what I have to say upon particular muscles, till I have related some facts relative to the nerves.