42 Land and Freshwater Animals 



Small aquatic organisms may sometimes be easily collected and con- 

 centrated by the use of the following simple field or laboratory device. 

 Attach a piece of rubber tubing of appropriate size and length to the 

 stem of an ordinary, medium-sized glass funnel. Stretch across the open 

 end of the funnel a piece of India linen, bolting cloth, grit gauze, or 

 similar material, the mesh of which is such that the organism desired will 

 not pass through, and hold in place with a rubber band or cord. Fill a 

 pail with water. Place the funnel, wide end down, in the pail but leave 

 the longer part of the rubber tubing outside the pail, the free end 

 extending below the level of the bottom. Apply momentary suction 

 at the free end of the rubber tubing to convert the latter into a siphon 

 which will drain the water through the gauze-covered funnel to the 

 outside. 



By pouring the water containing the desired organisms into the pail 

 the water is gradually eliminated through the funnel but the organisms 

 are retained. This process may be continued until the desired concentra- 

 tion of the organisms in the pail is reached. 



A cover of wire cloth of wider mesh may be placed over the pail to 

 exclude from the catch all larger animals and coarser trash. 



For collecting plankton a standard plankton net may be used (Fig. 

 15). If samples for qualitative study only are wanted, a simpler, less 

 expensive, and less cumbersome net is more practical. It may be made 

 by anyone and consists only of a regularly tapered bag of silk bolting 

 cloth attached by a topband to a rather heavy circular rim of non-rusting 

 metal. The bag may be 2 or 2% feet deep and its bottom should allow 

 easy eversion for the removal of the catch. A cord is attached to the 

 rim for towing. 



Removal of the catch in such a net may be facilitated by inserting a 

 vial of appropriate size and shape into a small hole at the end of the 

 bag. Held in place by a rubber band or a stout thread, such a container 

 may be removed easily after the collection is completed. 



If made of No. 25 standard silk bolting cloth, the net will retain all 

 but the minutest of the organisms (nannoplankton), but when drawn 

 through the water it will clog quickly, pushing much water aside without 

 straining it. No. 12 cloth, while not retaining things so small, will strain 

 more water and yield a bigger catch of the forms more generally useful 

 in the zoological laboratory. 



Small aquatic animals may be taken up on a lifter if not too delicate, 

 but they should not be exposed to the air for any considerable length of 

 time. In general the more delicate among them are better transferred by 

 means of a pipette, without exposure to the air. A hand bulb on a tube 

 may be used for the larger entomostracans. 



For isolating single unicellular algae for the production of pure 



