The question may well be asked: ‘Which is the best gum to use?’ In answer to this we may say that gum tragacanth is certainly as good as any. It holds well, and leaves no visible stain on a white card. A small quantity of the solid gum should be put into a bottle with water in which a grain or so of corrosive sublimate has been dissolved. It absorbs much water, becoming a very soft, jelly-like mass. Any excess of water may be poured off, and the gum is then ready for use. The larger crabs and lobsters contain such an amount of soft tissue within that it becomes absolutely necessary to clear them in order to avoid the unpleasant and destructive effects of decomposition. [Illustration: FIG. 43.--SMALL CRAB MOUNTED ON A CARD] In the case of lobsters the abdomen should be removed from the large cephalo-thorax by cutting through the connecting membrane with a sharp knife. The soft portions of both halves of the body are then raked out by means of a piece of wire flattened and bent at one end, and the interior cleaned with the aid of a rather stiff bottle-brush. The large claws are then removed by cutting through the membrane that unites them with the legs, and these are cleared in a similar manner. The different parts are next laid out to dry on blotting-paper, with the various appendages attached to the body arranged just as in life; and, finally, when all parts are quite dry, both within and without, the separated parts are reattached by means of some kind of cement. For this purpose a solution of gelatine in acetic acid is much better than gum tragacanth, as it has a far greater holding power, and this is necessary when we require to unite rather large structures with but small surfaces in contact. Large crabs are to be dealt with much in the same manner, but, instead of removing the abdomen only, which, in the crab, is usually very small and doubled under the thorax, the whole carapace--the large shell that covers the entire upper surface of the body--should be lifted off, and replaced again after the specimen has been cleaned and dried. MARINE SHELLS &C. We have previously dealt with the preservation of the shell-less molluscs, and the soft bodies of the shelled species when such are required, so we will now see what should be done with the shells.