MITOSIS. 37 
This is the egzal mitotic division, but in certain cases 
a reducing division occurs. In a reducing division the 
mitotic phenomena are much the same, but ¢he chromo- 
somes do not divide into two, hence the resulting daughter 
nuclet have only half the number of chromosomes of the parent 
nucleus. 
It is difficult to see the full meaning of mitosis, but 
it has been interpreted as a process for ensuring the 
equaé division of the chromatin. The astrospheres appear 
to act as centres of attraction for the chromosomes, and 
there can usually be discerned a nuclear spindle uniting 
the rays of the two astrospheres, giving the whole the 
appearance of a magnetic field. 
The reducing division is characteristic of gonogenests, or 
the production of the sexual elements. The primitive germ- 
cell produces sperm-mother cells, or egg-mother cells, which 
at the moment of division contain twice the number of 
chromosomes. Two rapid reducing divisions then produce 
four sperm cells in the male, or the mature ovum and polar 
bodies in the female... Hence the mature ovum and the 
spermatozoon have in their nuclei (¢ and 2 pronucleus) just 
half the normal number of chromosomes. When fused 
they produce a normal nucleus with the full number. 
The student should compare this account carefully with 
that given in Chapter V., page 42, and it will be clear that 
the reducing divisions and the enumeration of the chromo- 
somes lead to the same conclusion, namely, that the male 
and female elements (spermatozoon and mature ovum) are, 
morphologically speaking, merely half-cells produced by two 
rapid divisions at the limit of growth instead of the normal 
single division. 
