prometaphase

[prō-mĕtə-fāz′]
n.
  1. The stage of mitosis or meiosis in which the nuclear membrane disintegrates, the centrioles reach the poles of the cell, and the chromosomes continue to contract.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.