6. The fertilised ovum, with 4 chromosomes, 2 of paternal origin and 2
of maternal origin.
7. The chromosomes lie at the equator, and each is split longitudinally.
The centrosome introduced by the spermatozoon has divided into two
centrosomes, one at each pole of the nucleus. These play an important
part in the division or segmentation of the egg.
8. The fertilised egg has divided into two cells. Each cell has 2
paternal and 2 maternal chromosomes.]
[Illustration: _Reproduced from the Smithsonian Report, 1917._