In a good locality an expert diver may bring up fifty okes in a day, and for each oke he obtains about twenty-five drachmas. The weight is calculated, says Forbes, when the sponges are dry, and a very large sponge may weigh two okes. The chief sponge-markets are Smyrna. Rhodes, and Napoli. Blount, who wrote in 1634, affirms that these sponge-divers "are from infancy bred up on dry biscuites and other extenuatinge dyet, to make them extreme lean; then takinge a spunge wet in oyle, they hold it, part in their mouths, and part without, soe they go under water, where at first they can not stay long, but after practice, the leanest stay an hour and a halfe, even till the oyle of the spunge be corrupted.... Thus they gather spunges from more than an hundred fathom deep," &c. All this is very wonderful, but the narrator stamps the value of his tale by telling us immediately afterward that "Samos is the only place in the world on whose rocks the spunges grow." So that, in the words which he elsewhere makes use of, "we applaude hys belief, but keep our owne." We do not, however, mean to assert that there are not sponges of some species (though not the sponge of commerce) which exist at a depth as great as that which he mentions, for Forbes dredged a living specimen of one small kind from 185 fathoms in the Gulf of Macri. The sponge of commerce (_Spongia officinalis_) was divided by Aristotle into three kinds--namely, the loose and porous, the thick and close, and the fine and compact. These last, which are rare, were called the sponges of Achilles, and were placed by the ancients in the interior of their helmets and boots, as protections from pressure and abrasion. The same naturalist states that those sponges are best which are found on coasts where the water becomes suddenly deep, and attributes this superiority to the greater equality of temperature obtained in such waters--observations which have been corroborated by Professor E. Forbes. Fifty-six species of sponges have been enumerated, ten or eleven of which are found in the British isles. A portion of these inhabit fresh water, among which we may mention the river sponge (_S. fluviatilis_), which abounds in the Thames. Among the British sponges, too, is the stinging or crumb-of-bread sponge (_S. urens_), a widely-diffused species, which, when taken out of the sea is of a bright orange color, and which will, if rubbed on the hand raise blisters. This stinging quality is highly increased by drying the sponge; a process which also gives it the color and appearance of crumbs of bread, whence its popular name.