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How to Know Shells — Part 1

ALL up and down the ocean border, east and west and south, I have met people picking up shells. Children and grown people both give themselves to the eager search for ocean treasures left by the outgoing tide. The fascination of the pursuit--who has not yielded to it? Who ever came back from a walk on the beach without at least a handful of shells too irresistibly pretty or interesting to leave?

Ask the name of a shell and the reply is almost invariably: "It's some kind of clam," or, "It's some kind of snail." Few grown people regard with any feeling but distaste, if not disgust, "the slimy thing inside." Apparently they distrust the statement that the shell is but the skeleton of the living mollusk it protects.

It is not surprising that a popular misconception exists as to the origin of shells. Even scientists devoted to conchology used to discard the soft parts without considering their structure. The shell was the thing. On its characters alone classification was based. Now the whole mollusk is the thing, shell and all. The name is from the Latin adjective mollis, which means soft. Some mollusks have no shells at all. Most of them have shells for protection of their soft bodies, but they do not build them, as bees make comb of wax and the white-faced hornet builds her paper palace. Mollusks are shell-builders in the same sense that you and I are bone-builders. The fleshy mantle of the mollusk secretes lime from the water and adds it, layer by layer, to the growing shell. The horny skin outside and the pearly or enamel lining protect the shell substance from the corrosive action of acids in the water.

When we consider how little was known a hundred years ago about plants and animals compared with what the century has added; and when we think how changed is the attitude of scholars toward sciences to-day, we may well marvel that so much has been accomplished in so short a time. Science for its own sake is no such real and vital thing as science in its relation to human life. A great popular interest in natural sciences has followed the lead of scientists. Generations of Nature-lovers are coming on.

Conchology, as the name confesses, was the science of shells. In 1800 two thousand species of shells were known. Now fifty thousand species of mollusks are distinguished by name. The whole specimen is studied to determine its relationships. Its life history and habits are eagerly investigated. Thus has a dead science come to life; and we shall see people opening their eyes more and more to the wonderful forms of molluscan life that are all about them, but which they have not yet learned how to see.

The scope of the Mollusca is great. No other animal group has so wide and varied a range of distribution. All latitudes have their peculiar genera and species, excepting only the extreme polar regions. Land shells range from tide water to snowy mountain tops, to the limits of animal and vegetable life. Lakes and rivers teem with fresh-water forms. Amphibious mollusks cluster where land meets water. From the populous ocean border a diminishing list of marine forms live on the ocean bed to abyssmal depths. The pelagic mollusks live on the surface of the open sea.

Mollusks there are that climb, leap, crawl, burrow, swim, dive, float, even fly; for the graceful sea arrow which darts out of water like flying fish, is a squid, and squid are mollusks. There is no mode of locomotion denied them. From microscopic forms they range in size to the ponderous spindle-shell, a marine snail two feet long, and the giant clam, four feet across, weighing five hundred pounds.

As scavengers on the ocean border and inland, mollusks are important agents of sanitation, destroying disease germs in decaying organic matter, thereby purifying water and air. snails destroy noxious fungi and weeds. Mollusks furnish food to man and other animals. To a large extent they are the food of cod and other fish. Our dependence upon them is no less a fact because it is indirect, as in this case.

Oysters are preeminent among edible mollusks, with clams and cockles, and snails and scallops in a long train after them. An oyster is preeminent, too, as the source of the world's wealth in pearls. Mother-of-pearl is the lining of shells. Pearl buttons are cut from shells of the fresh-water clams. Cameos are cut from conchs and helmet shells. Sepia ink and the far-famed Tyrian dyes are molluscan secretions. Royal robes were woven of the threads by which the little pen shell clings to its rocky abode. A little cowrie of handy size and shape is the "money shell" of African tribes, the currency used in all traffic. But these interesting mollusks we can only read about. There are others closer by.