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A Microscopic Trap for a Rover.—If you would set aside a special corner for Practical Hints in Microscopic Manipulation, I, for one, should turn to if first on opening your journal. We all of us learn something in practice worth recording. Your correspondent S. S. R. has kindly sent me a rich collection, containing amongst others Hydatina Senta, (see Dr. C. T. Hudson's, paper 2 M. M. J. 22,) a rotifer which, if it has room for its vagaries, is the maddest of rovers, delighting chiefly in balancing itself on one toe and pirouetting as hard as it can turn in a vertical position! I first tried my usual cell, a ring of microscopic glass, the very thinnest I can get, (and answering to the number 6 on the adjustment collar of the ⅛th.) with a piece of glass as thin as itself over it. This prevented the whirligig performance, but rest was out of the question, and following even Hydatina’s charms under a ¼ gets monotonous when you are always only just catching her up. So I tried an old idea in a new form. I took a flat glass slide and dropped two Hydatinas on it, with a small drop of water about ½in, in diameter. Upon this drop I laid some cotton wool, frayed out so as to be much diluted with (I suppose I ought to say diffused in) space, I then put the thin sheet of glass on that, gave the thin sheet a touch with a needle to set the capillary attraction up, and Hydatina's gambols were over. I used a ⅛th to examine her easily. The wool acts as a prison to the animal, and a protection from pressure. I had restrained the little beauty as completely as a driver holds a well-broken horse. As the water evaporated a drop added at the side ran in and made all things comfortable again, and I have the two specimens still safe and back in their original bottle. I first tried a trap like this, sore years ago, on an animal of extraordinary character. It was related to the Poduras, I believe, but I have missed fixing its name—perhaps you can help me to it. It lived in a ditch—gregarious—hopping on the water perpetually, and most difficult to watch, about 1-10th of an inch long. There was no keeping it still a minute, so I improvised, in a deepish glass ring, a forest of cotton wool for it to ramble in, and the effect was most successful—I saw the instrument which gave it its extraordinary power of jumping actually in action. It consists of an enormous stumpy muscular organ, with a round cleft end. If is concealed in, and comes at will in and out of the centre of the under side of the abdomen; it gripped a piece of the wool with the cleft end, pinching it, and then by a violent effort—the exact nature of which I was unable fully to examine—it made its leap. The relative size of the organ, as compared with the abdomen, was something enormous—my notes say as 1 to 3, and it must have been very nearly that. Now, but for my wool trap I should have been quite baffled by both animals, for the compressorium is uncertain and difficult to manage, and, when successful, too often creates unnatural attitudes. I offer these hints with some confidence to your readers, and shall be grateful in return for a few practical hints on my own weak point, which is “light."—nowrap, Fort Hall, Bridlington Quay, Yorkshire. [We shall be much obliged to any microscopical readers who will act on Mr. Bedwell's hint and send us accounts of their methods of manipulation.—Eds. M.N.)

London Notes from an Occasional Correspondent.—Let me congratulate you on the near commencement of the Birmingham Aquarium, and express a fervent hope that the mistake too frequently made of considering the building first, and then consulting the scientific constructor, may not be fallen into, but that the Naturalist shall advise as to the Architect's plans before they are accepted. I am sorry to add that precautions are necessary to prevent the wanton or thoughtless cruelty practised towards the animals by visitors. A short time ago a gentleman was nearly knocked down by an electric eel which be seriously injured; then the