Do we not see in this astonishing example a highly successful effort of a marine worm to improve on the condition and habits of its barbarous ancestors? Analyse a bulk sample of the building material, and you shall find it not dissimilar from the shell of a mollusc, and the interior film--no doubt a secretion of the animal--is to be safely accepted as analogous to the silky smoothness which molluscs (often of rough and rugged exterior) obtain by nacreous deposit and which finds its culmination in the goldlip mother-of-pearl? Still higher in the series, so far as the construction of a tenement is concerned, is that known as the SERPULA, a worm which constructs a calcareous tube more or less loosely convoluted and adherent to a shell or stone or coral, or sometimes entwined into a self-supporting colony. Another worm builds of sand or mud, with a rough casting of fine gravel and shell-grit, a habitation similar in design to that of the serpula, though on a less complete and authoritative model; indeed, it would almost seem that the latter had designed its tenement after the fashion of that of its poor relation--that the one made a study in mud which the other reproduced in carbonate of lime. But the most curious fact is that a true mollusc (VERMETUS) so far departs from the fashion prevalent in the molluscan world of building a spiral shell, that after beginning one in proper spiral mode it elongates itself in vermiform manner and forms an irregular serpuloid tube on the surface of larger shells or stones just as the SERPULA does; so that without examination of the animal one may easily be mistaken for the other. What a contrast is here--on the one hand a lowly worm learning to build a solid if rude shelly covering for its tender body, on the other a relative of the elegant, many-whorled TURRITELLA forgetting its high station and degenerating to the likeness of a worm. No doubt it is really a case of degeneration from the acquirement of fixed habits, just as when a lively young crustacean larva gives up its free independent life and glues its head to a stone--what happens? Why, he becomes a mere barnacle instead of a spritely shrimp as he might have been! Let mankind take note and beware.