COLLECTING AND PRESERVING MATERIAL. 173 



Centipedes may be found by turning over flat 

 stones or logs, or pulling loose the bark from dead and 

 decaying stumps and trees. 



Crawfish may be captured with a minnow seine, 

 or caught with bait. A piece of liver as large as a 

 man's fist is tied to a string and thrown into the 

 stream. Crawfish cluster over it and cling to it, even 

 when drawn above the water. A net or dredge gently 

 slipped under the combination of liver and crawfish 

 will prevent the escape of many. Crawfish should be 

 boiled before being put into strong alcohol. 



Sow BUGS are to be looked for under boards or 

 other articles that lie on the ground. They are found 

 only in damp places. 



Tadpoles are collected from ponds in early spring. 

 It is well to collect a supply of toad eggs, frog eggs, 

 young tadpoles that show the gills, larger tadpoles for 

 dissection, and tadpoles that show the legs in various 

 stages of development. If some frog eggs or toad eggs 

 are discovered that are freshly laid, or better, if a 

 female is confined in a jar at the time when the eggs 

 are deposited, the different stages in the egg develop- 

 ment may be obtained. Two-celled, four-celled, eight- 

 celled, sixteen-celled, and thirty-two-cellad stages are 

 all easily recognized with a simple lens. 



Toad eggs and all other soft material are best pre- 

 served in formalin. This can be obtained from drug 

 stores for about sixty cents a pound. Four per cent of 

 formalin has been found a very satisfactory strength 

 for laboratory use. Dilute one pound of formalin 

 with about twenty-four pounds of water. Put it into 

 fruit jars and drop frog eggs, tadpoles, and sucli ma- 

 terial into it. This makes.an effective preservative for 

 less than twenty-five cents a gallon. 



Frogs and toads are preserved also in formalin. 



Fish may be captured in the fishing season and 

 preserved in the same way, but if the school is near a 



