\Pro*nu"cle*us\, n.; pl. {Pronuclei} (-[imac]). [NL.
See {Pro-}, and {Nucleus}.] (Biol.)
One of the two bodies or nuclei (called male and female
pronuclei) which unite to form the first segmentation nucleus
of an impregnated ovum.

Note: In the maturing of the ovum preparatory to
      impregnation, a part of the germinal vesicle (see
      {Polar body}, under {Polar}) becomes converted into a
      number of small vesicles, which aggregate themselves
      into a single clear nucleus. which travels towards the
      center of the egg and is called the female pronucleus.
      In impregnation, the spermatozo["o]n which enters the
      egg soon loses its tail, while the head forms a
      nucleus, called the male pronucleus, which gradually
      travels towards the female pronucleus and eventually
      fuses with it, forming the first segmentation nucleus.