“And then what a loud murmur it makes,” added Emile. “Is it true, Uncle, that it is the noise of the sea echoed by the shell?” [Illustration: Spiny Mollusk] “I do not deny that it resembles a little the murmur of waves heard at a distance; but you must not think that the shell keeps in its folds an echo of the noise of the waves. It is simply the effect of the air going and coming through the tortuous cavity. “This other belongs to France. It is common on the shores of the Mediterranean and belongs to the genus _cassis_.” “It goes _hoo-hoo_, like the helmet,” Emile remarked. “All those that are rather large and have a spiral cavity do the same. “Here is another which, like the preceding, is found in the Mediterranean. It is the spiny mollusk. The creature that inhabits it produces a violet glair, from which the ancients derived, for their costly stuffs, a magnificent color called purple.” [Illustration: Paludinidæ] “How are shells made?” asked Claire. “Shells are the dwellings of creatures called mollusks, the same as the spiral snail’s shell is the house of the horny little animal that eats your young flowering plants.” “Then the snail’s house is a shell, the same as the beautiful ones you have shown us,” Jules observed. “Yes, my child. It is in the sea that we find, in greatest number, the largest and most beautiful shells. They are called sea-shells. To these belong the helmet-shell, cassidula, and spiny mollusk. But fresh waters, that is to say streams, rivers, ponds, lakes, have them too. The smallest ditch in our country has shells of good shape but somber, earthy in color. They are called fresh-water shells.” “I have seen some in the water resembling large, pointed, spiral snails,” said Jules. “They have a sort of cap to close the opening.” “They are Paludinidæ.” “I remember another ditch shell,” said Claire. “It is round, flat, and as large as a ten or even twenty-sou piece.” [Illustration: Planorbinæ] “That is one of the Planorbinæ. Finally, there are shells that are always found on land and for that reason are called land-shells. Such is the spiral snail.” “I have seen very pretty snails,” Jules remarked, “almost as pretty as the shells in this drawer. In the woods you see yellow ones with several black bands wound round them in regular order.” “The creature we call the spiral snail—isn’t it a slug that finds an empty shell and lives in it?” asked Emile. “No, my friend; a slug remains always a slug without becoming a snail; that is to say, it never has a shell. The snail, on the contrary, is born with a tiny shell that grows little by little as the snail grows. The empty shells you find in the country have had their inhabitants, which are now dead and turned to dust, only their houses remaining.” “A slug and a snail without its shell are very much alike.”