There are two other species, the spatangus, and
the so-called bryssus, these animals are pelagic and scarce.
Further, there are the echinometrae, or 'mother-urchins', the
largest in size of all the species. In addition to these there is
another species, small in size, but furnished with large hard
spines; it lives in the sea at a depth of several fathoms; and is used
by some people as a specific for cases of strangury. In the
neighbourhood of Torone there are sea-urchins of a white colour,
shells, spines, eggs and all, and that are longer than the ordinary
sea-urchin. The spine in this species is not large nor strong, but
rather limp; and the black formations in connexion with the mouth
are more than usually numerous, and communicate with the external
duct, but not with one another; in point of fact, the animal is in a
manner divided up by them. The edible urchin moves with greatest
freedom and most often; and this is indicated by the fact that these
urchins have always something or other on their spines.
All urchins are supplied with eggs, but in some of the species the
eggs are exceedingly small and unfit for food. Singularly enough,
the urchin has what we may call its head and mouth down below, and a
place for the issue of the residuum up above; (and this same
property is common to all stromboids and to limpets).
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