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Although it is possible in some species of echinoids to distinguish the sexes by external characteristics (see the papers by Marx, 1932, and Harvey, 1956b), no differentiating characteristics have, as yet, been described for the American sea urchin, Arbacia punctulata. The sexes are readily identified after the animals are opened, by the deep red or purple ovaries and the white testes, or, if unopened animals shed spontaneously, by the red eggs and the white sperm. Hermaphroditic animals are occasionally found (Boolootian and Moore, 1956).
At Woods Hole, Mass., the animals are obtained by dredging; they are, at the present time, rather scarce.
An exhaustive account of the life-history, embryology and metamorphosis of Arbacia is given by Harvey (1956a).