The Collaborative International Dictionary of English v.0.48:

Cytoblast \Cy"to*blast\ (s?"t?-bl?st), n. [Gr. ky`tos hollow
   vessel + -blast.] (Biol.)
   The nucleus of a cell; the germinal or active spot of a
   cellule, through or in which cell development takes place.
   [1913 Webster]