THE NATURAL HISTORY SURVEY. 31 
tion. Each tray of specimens should be numbered and entered 
in the catalogue, together with all possible information. A 
card catalogue is also of great value. 
4. PRESERVATION FOR ANATOMICAL USE.* 
It is sometimes desirable to preserve the soft parts of mol- 
lusks for anatomical and microscopical use. This may be done 
in the following manner: Land and fresh-water gastropods 
may be killed by drowning, which can be done by putting them 
in an air-tight vessel filled completely with water so as to ex- 
clude all the air. By this means the soft parts will be more 
extended than if killed by boiling water, as recommended for 
cabinet specimens. They should then be gradually hard- 
ened as follows: Thirty per cent. alcohol, twenty-four hours; 
seventy per cent. alcohol, thirty hours, and eighty-five per cent. 
alcohol for final preservation. A one per cent. solution of 
chromic acid makes a good reagent, and the object, if not too 
large, may be left in it for twenty-four or thirty hours, after 
which they should be thoroughly washed in running water for 
twenty-four hours until the acid is removed. 
It is of great importance that the radula or lingual ribbon 
should be preserved for study. This is a strap or belt of chiti- 
nous or horny matter, occupying the place in the mouth of the 
animal analogous to that occupied by the tongue in the verte- 
brates. The apparatus is protrusile and may be studied .by 
feeding a snail, Limnza stagnalis for example, soft crumbs of 
bread. In the larger forms it may be found with but little 
trouble, but the smaller forms must be boiled in caustic potash. 
This is accomplished as follows: Extract the animal from its 
shell and place in a test tube containing a tablespoonful of 
caustic potash which has become liquid by the attraction of 
atmospheric moisture. Hold the test tube at the side of the 
flame of an alcohol lamp until it boils, being careful not to let 
it boil over and that the animal matter is not thrown out of the 
liquid on to the dry side of the tube; if this happens dislodge 
it by shaking the liquid over it. Boil slowly until the animal 
matter is dissolved, then pour it out quickly into a watch crys- 
tal, refill the test tube with water and pour into another watch 
crystal. Give the first crystal a rotary motion, not too violent, 
so as to bring the solid particles to the center. Examine with 
a powerful hand lens; a sheet of white paper under the watch 
*See Dall, |. c., p. 43. 
