ance of the achromatin substance
between the two groups of chromatin loops is observable (H). In
some cases (especially egg-cells) this striated arrangement of the
achromatin is then termed a "nucleus-spindle," and the group of
chromatin loops (G, _a_) is known as "the equatorial plate." At
each end of the nucleus-spindle in these cases there is often seen
a star consisting of granules belonging to the general protoplasm
of the cell (G, _c_). These are known as "polar stars." After the
separation of the two sets of loops (H) the protoplasm of the
general substance of the cell becomes constricted, and division
occurs, so as to include a group of chromatin loops in each of the
two fission products. Each of these then rearranges itself together
with the associated chromatin into a nucleus such as was present in
the mother cell to commence with (I)[13].

[13] Ray Lankester, _Encyclop. Brit._, 9th ed., Vol. XIX, pp. 832-3.

Since the above was published, however, further progress has been made.
In particular it has been found that the chromatin fibres pass from
phase D to phase F by a process of longitudinal splitting (Fig. 37 _g_,
_h_; Fig. 38, VI, VII)--which is a point of great importance for
Weismann's theory of heredity,--and that the protoplasm outside the
nucleus seems to take as important a part in the karyokinetic process as
does the nuclear substance. For the so-called "attraction-spheres" (Fig.
38 II _a_, III, III _a_, VIII to XII), which were at first supposed to
be of subordinate importance in the process as a whole, are now known to
take an exceedingly active part in it (see especially IX to XI). Lastly,
it may be added that there is a growing consensus of authoritative
opinion, that the chromatin fibres are the seats of the material of
heredity, or, in other words, that they contain those essential elements
of the cell which endow the daughter-cells with their distinctive
characters. Therefore, where the parent-cell is an ovum, it follows from
this view that all hereditary qualities of the future organism are
potentially present in the ultra-microscopical structure of the
chromatin fibres.

[Illustration: FIG. 37.--Study of successive changes taking place in
the nucleus of an epithelium cell, preparatory to division of the
cell. (From _Quain's Anatomy_, after Flemming.) _a_, resting cell,
showing the nuclear network; _b_, fi