On Excavations Made in Rocks by Sea-Urchins

Abstract

The results of the preceding pages may be briefly stated as follows: 1. Strongylocentrotus drobachiensis on the coast of Grand Manan sometimes makes excavations in solid rock. 2. The excavations are made by the sea-urchin by means of its teeth, spines, combined with motions of tile animal produced by waves and tide. The object is primarily for protection, but secondarily a sufficient amount of water is in that way retained by the animal during half tide, or when otherwise uncovered. 3. The coralline accompanying the sea-urchin, generally found at the rim of the excavation, takes no part in the formation of the recess, although its presence may be necessary to the animal for some unknown reason. 3. Sea-urchins are found at Biarritz, France, which live in stories on the walls of peculiar pot-holes, some of which have a central style also tenanted by the same animals in small depressions. 5. The sea-urchins play some part in the formation of stylated pot-holes, although they are assisted by the movements of stones, produced by the action of tides and waves.