THE NATURAL HISTORY SURVEY. 29 
well, however, and even a good sized tumbler will answer the 
purpose. 
Care should be taken to record all observations, as much 
information is needed concerning the embryological ‘develop- 
ment of the fresh-water mollusks. 
38. PRESERVATION OF COLLECTIONS. 
The preservation of the collections obtained on each day’s 
trip is of great importance, for upon this depends the appear- 
ance and value of the collector’s cabinet. When the specimens 
are collected they are covered with mud and growths of various 
kinds, and must be thoroughly cleaned. In the case of land 
and fresh-water shells, they should first be washed clean of 
mud, etc.; this may be rendered easier by the aid of a tooth- 
brush. The soft parts may be removed by putting the animal 
for a few seconds in boiling water. If they are first placed in 
lukewarm water for a few minutes and then transferred to the 
boiling water it will prevent cracking and preserve the polish 
which is frequently lost when delicate shells are immediately 
placed in boiling water. Theanimal may be extracted from the 
shell with a crooked pin or wire, or better still, a small pair of 
tweezers. Those species having an operculum should have 
it carefully removed and attached to a piece of cotton, which 
may be placed in the aperture of the shell. Some opercula 
warp out of shape while drying, and it will be found a good 
rule to place them between two boards during this process. 
Some of the shells may be covered with incrustations of lime 
and peroxide of iron, and to remove these an old file or small 
bone scraper will be found useful. The file should be 
ground to a point. Naked mollusks (slugs) may be pre- 
served in alcohol or formalin. The internal shell of Limax may 
be extracted and preserved if desirable, but the better method 
is to prepare the whole animal. Shells that are stained with 
iron or other matter may be perfectly cleaned by placing for a 
few moments in a solution of oxalic acid. 
Unios and other bivalves should have the animal removed 
with a flat-bladed knife. To do this the two adductor muscles 
must be cut, after which the valves will open and the animal 
may be entirely cut away. If the shells are left in the sun for a 
few hours they will gape and the animal may then be easily 
removed. The two valves should be tied together in their nat- 
ural position. Care should be used in cleaning the shell so 
