The urchins

are devoid of flesh, and this is a character
peculiar to them; and while they are in all cases empty and devoid
of any flesh within, they are in all cases furnished with the black
formations. There are several species of the urchin, and one of
these is that which is made use of for food; this is the kind in which
are found the so-called eggs, large and edible, in the larger and
smaller specimens alike; for even when as yet very small they are
provided with them. 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.