The Collaborative International Dictionary of English v.0.48:

Centrosphere \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.
      [Webster 1913 Suppl.]

   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.
      [Webster 1913 Suppl.]