\Cen"tro*sphere\, n. [Gr. ? centre + sphere.]
1. (Geol.) The nucleus or central part of the earth, forming
   most of its mass; -- disting. from {lithosphere},
   {hydrosphere}, etc.
2. (Biol.) The central mass of an aster from which the rays
   extend and within which the centrosome lies when present;
   the attraction sphere. The name has been used both as
   excluding and including the centrosome, and also to
   designate a modified mass of protoplasm about a centrosome
   whether aster rays are developed or not.