Vorticella, or the trumpet animalcules, Stentor, or similar forms. Small snail 

 shells often carry such a collection, usually all of one species. Even such 

 rapidly moving animals as the crayfishes and scuds furnish temporary or 

 permanent caravans for Proto-oa. Hydras very often carry one or more kinds 

 of ciliated, commensal Protozoa. The amoeboid forms are more likely to be 

 found on the bottom oo;c or on the under sides of old water-lily leaves. Since 

 they can survive more acid conditions than can most of the flagellates and 

 ciliates, they can often be most easily collected in boggy or marshy ponds and 

 cat-tail swamps. 



A good method of collecting is to dip a jar into the water and push into 

 it some of the water plants, dead and alive, without first lifting them from 

 the water. Another method is to use a fairly large container and "wash" 

 several handfuls of water plants in it. Many of the minute animals can thus 

 be washed off and concentrated, most of the weed being discarded. For the 

 larger forms a plankton net may be used, or pond water poured through a 

 piece of silk and the "strainings" washed otf into the collecting bottle. Special- 

 ized equipment, such as the plankton pump, is available for qualitative and 

 quantitative studies. 



Collections should be made at different hours of the day, and in both 

 sunny and shaded places, as each species has its optimum of temperature and 

 light, and a continuous movement takes place as the different forms seek the 

 optimum conditions. Those with chlorophyll usually prefer the sunny areas, 

 v.-hile those not green or brown avoid bright illumination. 

 Care and study 



Material brought in from the field should be placed in shallow dishes in 

 a fairly well lighted and cool place not in direct sunlight. Some green water 

 plant will aid in maintaining favorable conditions but care should be taken 

 to avoid a surplus which will rot and spoil the whole collection. If any water 

 is added, it should not be chlorinated tap water or freshly distilled water, 

 which is usually acid. For any aquatic animals from Protozoa to fish, it is 

 usually advisable to "temper" the extra w-ater by allowing it to stand for 

 several hours in an open, non-metallic container near the aquarium or culture 

 to which it is to be added. Large containers make fatal fluctuations in tempera- 

 ture less likely but. w^here temperature is fairly constant and it is desired 

 to keep several collections separate, finger bowls or jelly glasses serve well and 

 are inexpensive. Crustaceans and insect larvae should be removed, if the 

 Protozoa are to survive. 



Examinations should be made at intervals over a considerable period of 

 time, for a succession of forms may appear, especially if the cultures are 

 large. At first only a few ciliate or flagellate forms may be found, but two or 

 three days later another batch of entirely different flagellates or ciliates may 

 appear in the same container, and after a week or two, when a succession of 



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