54 



HARDWICKE'S SCIENCE-GOSSIP. 



POND DREDGING AND COLLECTING. 



REPLYING to this query in the February 

 number, I have much pleasure in giving some 

 hints on collecting Infusoria, Rotifera, and Polyzoa, 

 the result of my experience in this interesting pursuit. 



The necessary apparatus are : a collecting stick, a 

 flat bottle, a pocket magnifier, and a handbag with 

 bottles. 



Of all the various collecting sticks I have seen, I 

 like none so well as the pattern supplied by Baker's, 

 of High Holborn ; it consists of a hollow walking- 

 stick, with an inner rod which can be drawn out to 

 increase its length, a small bottle, a hook, and a ring 

 for the net, all of which can be screwed on to the 

 stick. 



The net should be made of dense muslin, with 

 meshes small enough to prevent Rotifera and 

 Infusoria going through, and yet allowing the water 

 to run out freely. It is of some importance to have 

 exactly the right material ; as a guidance, I may 

 mention that on holding my net to the window I can 

 see the light through it, but no object with any 

 degree of distinctness, nor can I read through it ; 

 when taking a dip the water runs through in about 

 5 to 10 seconds. The net should not be too long, 

 nor too short ; 5 in. is a proper length, by 6 in. 

 across the ring ; at the end is tied a small rimmed 

 tube bottle of thin, clear glass, 3 in. long by I in. in 

 diameter ; a common bottle of thick glass would be 

 of very little use, because minute objects cannot be 

 seen through such a bottle. 



The flat bottle was first introduced by Mr. Hardy, 

 with the object of placing it under the microscope to 

 examine its contents. I seldom use it in that way, 

 because it is too inconvenient ; the stages of micro- 

 scopes are not large enough to hold it, and so it is 

 mostly necessary to hold and move it with both hands, 

 leaving none free to focus the microscope ; I prefer 

 to remove the weeds to a smaller trough. For use 

 in the field and collecting, however, it is a most 

 excellent contrivance, and quite indispensable. Every 

 one knows how impossible it is to see an object 

 clearly in a round bottle with a lens, whilst the flat 

 bottle allows this to be done with the greatest ease. 

 To make these bottles, get a thick piece of india- 

 rubber, quite fiat, about 6 to 6h in. long and 2J to 

 3 in. broad, and -j or f in. thick, then cut out an 

 inner piece all round, except at the top, at \ in. 

 from the edge, the result will be a |j -shaped piece of 

 indiarubber, against each side of which cement, with 

 Miller's cement, a piece of thin plate glass, and the 

 llat bottle is complete. One or two more and smaller 

 bottles can be made with the remaining piece of 

 indiarubber. I strongly recommend the indiarubber 

 to be if in. thick, so as to make a deep bottle, other- 

 wise the weeds, such as Anacharis, when put in with 

 much difficulty, are pressed against the glass, which 

 seriously interferes with their examination. 



The pocket lens should not be bi-convex, as is 

 usually the case, but plano-convex, and used with 

 the plane side towards the object. 



Having described the apparatus, I will now briefly 

 mention how to use them. 



For the purpose of collecting, the Infusoria and 

 Rotifera may be divided into two groups : the free 

 swimming and those that are attached to water plants. 

 For collecting the group of free swimming forms 

 there is no better device than the net ; pass it through 

 the water once or twice, and then hold it up and let 

 the water run out — the condensed animals will enter 

 the bottle quite at the last, like a cloud ; it is there- 

 fore wrong to take a second dip before all the water 

 has run out of the net. The ordinary dipping bottle, 

 without net, is also useful and sufficient when the 

 animals are abundant, but the net is certainly the 

 best way of condensing them. At the same time, it 

 is a mistake to condense pond-life too much, as the 

 animals soon exhaust the food supply and die. 



Having ascertained with the pocket lens that the 

 dip contains something, the contents of the tube is 

 poured into another bottle. Some collectors take 

 with them a number of small bottles for this purpose, 

 but I prefer to have two or three large ones, with 

 only one or two small ones, to be able to isolate an 

 object on the spot when required. 



The group of attached Infusoria and Rotifera are 

 best found with the flat bottle described above. 

 Drag up with the hook a quantity of weed, and, 

 selecting clean branches, but not the newest growth, 

 place one branch after another in the bottle, which 

 can then be carefully scrutinised with the lens. The 

 tubes of Melicerta and Polyzoa, groups of Vorticella, 

 etc., can at once be seen with the naked eye when 

 present, and the good branches can soon be picked 

 out. At the same time it must not be forgotten that 

 some minute and very transparent animals, such as 

 the Floscules, can rarely be seen even with the lens, 

 and only the microscope at home will reveal all the 

 captures. Experience alone can teach which of the 

 branches are most likely to be prolific. As a general 

 rule old-looking, but still sound and green, branches 

 are the best. The water milfoil (Myriophyllum) is 

 the best of water-plants to examine and collect, on 

 account of the ease with which it can subsequently 

 be placed under the microscope, Anacharis being a 

 very awkward plant in this respect. 



In placing a weed in the flat bottle never put in 

 more than one branch at a time, otherwise the 

 branches will only obscure each other, and render 

 examination more difficult. For Polyzoa it is best to 

 dredge up weeds from the middle of the pond or 

 canal by means of a loaded hook and line. 



Having selected the most promising branches out 

 of various ponds, I place them all in the large bottles 

 with the water to be taken home. Care must be 

 taken not to put too many weeds in the bottles ; in 

 the first place, no one has time to examine so much 



