valve downwards on the bottom of the phial. The first thing I observed was the thrusting forth of the delicate little foot, an organ which seemed to me appropriately named, when I marked its close resemblance in form to a human foot and leg, enveloped in a white stocking. What I may call the sole of this tiny foot was pressed against the side of the glass, feeling about from place to place; while with the lens I could distinctly see, in the part corresponding to the toe, the opening of the fleshy lips, or sides of the grooves, in which the threads of byssus are said to be formed. While it was thus engaged my surprise was excited by seeing it suddenly throw itself with a jerk into an upright position; but the action was too startling to allow me to see how it was performed. I again laid it prone, and though for a moment it closed the valves, it presently opened them again, and performed a similar feat. This was followed by several leaps in different directions, in quick succession; but I was still at a loss to know the modus operandi. It appeared to me certain, that the ordinary supposition, viz. that the action is performed by the vigorous opening and shutting of the valves, was not the correct one. At length a favourable observation gave me a suspicion of the truth. I perceived the lips of the mantle (which were held in contact, though the valves were considerably separated) suddenly open to a partial extent, as if by blowing from within. At this instant there was a leap in the opposite direction, attended with a considerable agitation in the water. With this clue I observed more definitely. Having rendered the water a little turbid, in order the more distinctly to see any motion of the particles
