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 oferciulum of such gasteropods as 
possess it, as it nas 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 (Strepomatidz, Viviparide, Limnzeidee, Unionidee 
and Cycladidz), 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. 
