The continental area is on one side of the sphere and the oceanic on the other.
The general scheme of oceanic circulation was made out prior to 1910.
wide areas, giving rise to oceanic depressions and leaving the continents protuberant; the other, folding along comparatively narrow belts, giving rise to mountain ranges.
the Pacific has few islands; the oceanic islands are volcanic, and coral formations are of course scanty.
The Trachylinae, on the other hand, are above all oceanic forms, and have no polyp-stage, and hence there is typically no alternation in their life-cycle.