42 NATURALISTS' ASSISTANT. 



has been found in which gasteropods can be so preserved, 

 though many experiments have been tried. Sea anemones, 

 etc., may be readily killed expanded by gradually adding 

 picric acid to the vessel in which they are contained. An- 

 other way is to allow them to die in sea water which has 

 become stale. The former method, however, is the most 

 successful. Fresh-water Polyzoa, it is said, may be killed in 

 an expanded condition by adding a few drops of alcohol or 

 brandy to the water in which they are living. 



Should it be desired to preserve the shell of a mollusk 

 without the animal, the whole may be macerated in water 

 and the contents carefully washed away. Bivalves should 

 have the two halves carefully tied together, while care should 

 be taken to preserve the opercuhim of such gasteropods as 

 possess it, as it has considerable systematic value. 



The same methods may be employed in collecting fresh- 

 water invertebrata as in marine. Ponds and lakes can readily 

 be dredged and a trawl or siene will frequently bring up 

 numbers of rare forms. The beds of rivers contain numer- 

 ous shells (Strepomatidae, Viviparidae, Limnaeidae, Unionidae 

 and Cycladidae) , for which careful search should be made. 

 A dipper, with a perforated bottom, on a long stick, is fre- 

 quently a handy substitute for a dredge, in shallow water. 



Land shells are most numerous in a limestone country. A 

 good place to hunt for them is under boards or fallen leaves. 



