108 CORRESPOXDENCE. 



A Microscopic Trap for a Rover. — If you would Bet aside a special 

 oomer for Practical Hints in Microscopic Manipulation, I, for one, should 

 turn to it first on opening your journal. Wo all of us learn something in 

 practice worth recording. Yo\ir coiTespondent S. 8. R. has kindly sent 

 me a rich collection, containing anaongat 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 1 I first tried my lasual cell, a ring of microscopic glass, the 

 very thinnest I can get, (and answering to the number 6 on the adjust- 

 ment collar of the ^th,) with a piece of glass as thin as itself over it. This 

 prevented the whirligig perfoiTuance, but rest was out of the question, 

 and following even Hydatina's charms under a J gets monotonoue 

 when you are always only just catching her tip. 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 ^in. 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 |th to 

 examine her easily. The wool acts as a prison to the animal, and a pro- 

 tection from pi'essure, 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, some 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 

 catch, about 1-lOth 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 extraordinai'y power of jumping actually in 

 action. It consists of an enormous stumpy muscular organ, with a 

 round cleft end. It 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 efl'ort — 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 some- 

 thing 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." — F. A. Bepwell, Fort Hall, Bridlington Quay, 

 Yorkshire. [Wc 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. — Eps. M.N.I 



London Notes from an Occasional Correspondbnt. — Let me con- 

 gratulate you on the near commencement of the Birmingham Aquarium, 

 and express a fervent hope that the mistake too frequently made of consider- 

 ing the buUdiug 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 pi'cvcnt the wanton or thoughtless cruelty practised towards 

 the animals by visitors. A short time ago a gentleman was nearly 

 knocked down l)y an electric eel which he seriously injured ; then the 



