The Agglutinating Top (_Trochus agglutinans_) covers itself with small stones and fragments of shells, and thus shielded from the view escapes the voracity of many an enemy but little suspecting the savoury morsel hidden under the mound of rubbish which he disdainfully passes by. In animals which are only provided with passive means of defence, we may naturally expect a considerable degree of caution, and in this respect the gasteropods might give many useful lessons to man. How carefully they protrude their tentacles as far as possible to sound every obstacle in their way, before they creep onwards, and how rapidly they withdraw into their shell at the least symptom of danger! What an example to so many of us that leap before they look, and frequently break their necks in the fall! Yet, in spite of all their prudence and of the protection of their stony dwellings, they serve as food to a host of powerful enemies. The sea-stars, their most dangerous foes, not only swallow the young fry but also seize with their long rays the full-grown gasteropods, and clasp them in a murderous embrace. They are preyed upon by fishes, crustaceans, and sea-birds, who pick them up along the shores; but it will sometimes happen that a crow, while endeavouring to detach a limpet for its food, is caught by the tip of its bill, and held there until drowned by the advancing tide. Man also consumes a vast number of sea-snails, for on every coast there are some edible species; and it may be said that, with the exception of very few that have a disagreeable taste, they are all of them used as food by the savage. The miserable inhabitants of Tierra del Fuego chiefly live upon a large limpet that abounds on the rocky shores of their inhospitable land, and but for this resource would most likely long since have been extirpated by hunger.