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.
