We had covered about two-thirds of the distance to the factory when the road approached a wide ditch; and from the attention with which my friend regarded it, I suspected that this was the something for which he had been looking. It was, however, quite unapproachable, for it was bordered by a wide expanse of soft mud thickly covered with rushes and trodden deeply by cattle. Nevertheless, Thorndyke followed its margin, still looking about him keenly, until, about a couple of hundred yards from the factory, I observed a small decayed wooden staging or quay, apparently the remains of a vanished footbridge. Here Thorndyke halted, and unbuttoning his coat, began to empty out his pockets, producing first the vasculum, then a small case containing three wide-mouthed bottles--both of which he deposited on the ground--and finally a sort of miniature landing-net, which he proceeded to screw on to the ferrule of his stick. “I take it,” said I, “that these proceedings are a blind to cover some sort of observations.” “Not at all,” he replied. “We are engaged in the study of pond and ditch natural history, and a most fascinating and instructive study it is. The variety of forms is endless. This ditch, you observe, like the one at Bantree, is covered with a dense growth of duck-weed: but whereas that ditch was swarming with succineæ, here there is not a single succinea to be seen.” I grunted a sulky assent, and watched suspiciously as he filled the bottles with water from the ditch and then made a preliminary sweep with his net. “Here is a trial sample,” said he, holding the loaded net towards me. “Duck-weed, horn-weed, Planorbis nautileus, but no succineæ. What do you think of it, Jervis?” I looked distastefully at the repulsive mess, but yet with attention, for I realized that there was a meaning in his question. And then, suddenly, my attention sharpened. I picked out of the net a strand of dark green, plumy weed and examined it. “So this is horn-weed,” I said. “Then it was a piece of horn-weed that Cyrus Pedley held grasped in his hand; and now I come to think of it, I don’t remember seeing any horn-weed in the ditch at Bantree.” He nodded approvingly. “There wasn’t any,” said he. “And these little ammonite-like shells are just like those that I noticed at the bottom of Dr. Parton’s jar. But I don’t remember seeing any in the Bantree ditch.” “There were none there,” said he. “And the duck-weed?” “Oh, well,” I replied, “duck-weed is duck-weed, and there’s an end of it.” He chuckled aloud at my answer, and quoting: “_A primrose by the river’s brim_ _A yellow primrose was to him_,”