rst stage of division, the
chromatoplasm transformed into a skein of closely contorted
filaments; _c_ to _f_, further stages in the growth and looping
arrangement of the filaments; _g_, stellate phase, or aster; _h_,
completion of the splitting of the filaments, already begun in _f_
and _g_; _i_, _j_, _k_, successive stages in separation of the
filaments into two groups; _l_, the final result of this (diaster);
_m_ to _q_, stages in the division of the whole cell into two,
showing increasing contortion of the filaments, until they reach the
resting stage at _q_].

[Illustration: FIG. 38.--Formation and conjugation of the pronuclei
in _Ascaris megalocephala_. (From _Quain's Anatomy_, after E. von
Beneden.) _f_, female pronucleus; _m_, male pronucleus; _p_, one of
the polar bodies.

I. The second polar body has just been extruded; both male and
female pronuclei contain two chromatin particles; those of the male
pronucleus are becoming transformed into a skein. II. The chromatin
in both pronuclei now forms into a skein.

II _a_. The skeins are more distinct. Two attraction (or
protoplasmic) spheres, each with a central particle united with a
small spindle of achromatic fibres, have made their appearance in
the general substance of the egg close to the mutually approaching
pronuclei. The male pronucleus has the remains of the body of the
spermatozooen adhering to it.

III. Only the female pronucleus is shown in this figure. The skein
is contracted and thickened. The attraction-spheres are near one
side of the ovum, and are connected with its periphery by a cone of
fibres forming a polar circle, _p.c._; _e.c._, equatorial circle.

III _a_. The pronuclei have come into contact, and the
spindle-system is now arranged across their common axis.

IV. Contraction of the skein, and formation of two U-or V-shaped
chromatin fibres in each pronucleus.

V. The V-shaped chromatin filaments are now quite distinct: the male
and female pronuclei are in close contact.]

[Illustration: (38 continued)

VI., VII. The V-shaped filaments are splitting longitudinally; their
structure of fine granules of chromatin is apparent in VII., which
is more highly magnified. The conjugation of the pronuclei is
apparently complete in VII. The attraction-spheres and achromatic
spindle, although