SHELL-CAMEOS., 297 
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 ten- 
tacles 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 fre- 
quently 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 tbe 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 Lunger. 
Many of the univalve shells are, moreover, highly prized as 
objects of ornament or use both by savage and civilised nations, 
The South Sea Islander makes use of a Triton as a war conch; 
the Patagonian drinks out of the Magellanic volute, the Arab 
of the Red Sea employs a large Buccinum as a water-jug, and 
the Cyprea moneta is well known in commerce as the current 
coin of the natives of many parts of Africa. In Europe the iri- 
descent Haliotis is frequently used for the inlaying of tables or 
boxes, and various species of Helmet-shells and Strombi (Cassis 
rufa madagascariensis, Strombus gigas), peculiar as being 
formed of several differently coloured layers, placed side by side, 
are in great request for the cutting of cameos, as they are soft 
enough to be worked with ease, and hard enough to resist wear. 
More than two hundred thousand of these shells are annually 
