both the pronuclei before their
junction is effected; and, even when their junction is effected, it does
not appear that complete fusion of the so-called chromatin elements of
the two pronuclei takes place. For the purpose of explaining what this
means, and still more for the purpose of giving a general idea of the
karyokinetic processes as a whole, I will quote the following
description of them, because, for terseness combined with lucidity, it
is unsurpassable.

[Illustration: FIG. 36.--Karyokinesis of a typical tissue-cell
(epithelium of Salamander). (After Flemming and Klein.) The series
from A to I represents the successive stages in the movement of the
chromatin fibres during division, excepting G, which represents the
"nucleus-spindle" of an egg-cell. A, resting nucleus; D,
wreath-form; E, single star, the loops of the wreath being broken;
F, separation of the star into two groups of U-shaped fibres; H,
diaster or double star; I, completion of the cell-division and
formation of two resting nuclei. In G the chromatin fibres are
marked _a_, and correspond to the "equatorial plate"; _b_,
achromatin fibres forming the nucleus-spindle; _c_, granules of the
cell-protoplasm forming a "polar star." Such a polar star is seen at
each end of the nucleus-spindle, and is not to be confused with the
diaster H, the two ends of which are composed of _chromatin_.]

Researches, chiefly due to Flemming, have shown that the nucleus in
very many tissues of higher plants and animals consists of a
capsule containing a plasma of "achromatin," not deeply stained by
re-agents, ramifying in which is a reticulum of "chromatin"
consisting of fibres which readily take a deep stain. (Fig. 36, A).
Further it is demonstrated that, when the cell is about to divide
into two, definite and very remarkable movements take place in the
nucleus, resulting in the disappearance of the capsule and in the
arrangement of its fibres first in the form of a wreath (D), and
subsequently (by the breaking of the loops formed by the fibres) in
the form of a star (E). A further movement within the nucleus leads
to an arrangement of the broken loops in two groups (F), the
position of the open ends of the broken loops being reversed as
compared with what previously obtained. Now the two groups diverge,
and in many cases a striated appear