in Dictyota dichotoma . 191 
Fig. 1. Nucleus in prophase with centrospheres on opposite sides; at the upper 
end the centrosome is seen from the side, that at the lower is seen from the end. 
Fig. 2. A somewhat later stage. Nucleus with surrounding cytoplasm and 
chloroplasts. The centrospheres are large, with dense radiations; the chromatin 
has collected in larger irregular masses; the nucleolus is very large and vacuolated. 
To the left within the nucleus are numerous fine granules. 
Fig. 3. The spindle-fibres have begun to penetrate the membrane and enter the 
nuclear cavity at the poles; chromatin masses large; nucleolus more finely 
vacuolate. At the poles the nuclear membrane is infolded, due probably to 
a slight shrinkage. 
Fig. 4. The cones of penetrating fibres are much larger; a few of the fibres 
have met at the equator to form the continuous spindle-fibres extending from pole 
to pole. The chromosomes are collecting in the region of the nuclear plate. The 
nucleolus has almost or quite disappeared, while numerous smaller but densely 
staining granules are present; a fine threadwork, presumably linin, is also to be 
seen. 
Fig. 5. A nearly mature spindle. The centrosomes are smaller and partly 
obscured by the numerous fine radiations and spindle-fibres centred upon them; at 
the sides the nuclear membrane is still preserved. 
Fig. 6. A mature spindle, showing chromosomes arranged regularly in equatorial 
plate, and the following orientation of spindle-fibres: those extending unin¬ 
terruptedly from pole to pole; the bundles of contracting fibres attached to the 
chromosomes and extending to the centrosomes; the mantle-fibres, or those 
diverging toward the nuclear membrane in the direction of the equator and the 
polar radiations. As in the two preceding figures traces of the nuclear membrane 
are visible at the sides. 
Fig. 7. One end of a karyokinetic figure in the anaphase. The chromatin 
masses never approach nearer to the centrosome. 
Fig. 8. Two daughter nuclei with surrounding cytoplasm ; the nuclear mem¬ 
branes have just been laid down; the chromatin is in the form of a lumpy mass, 
near which is a very evident nucleolus, and a linin network with granules is also 
present. The connecting fibres have nearly disappeared, while the polar radiations 
have become more pronounced and the centrosomes larger in size. 
Figs. 9-15. Division of the daughter nucleus. 
Fig. 9. Daughter nucleus at a little later stage than Fig. 8, more highly 
magnified. The centrosome has just divided, the segments having separated at 
one end, but still almost touching at the other, so as to form a shallow V-shaped 
figure. The attachment of the fibres to the daughter segments suggests that the 
former exert a pulling force upon the latter. 
Fig. io. A later stage in which the centrospheres have moved apart a short 
distance. The nucleus reveals the structure of the resting condition. 
Fig. ii. The beginning of the formation of the spindle; only one pole is shown, 
the other lying in the next section. As in the corresponding stage of the preceding 
division, the fibres of the spindle-cones are of unequal length, and the nuclear 
membrane is as yet unbroken. The nucleolus is vacuolate; the chromatin is 
represented by small but densely staining masses, and the linin is in the form of 
a small-meshed and finely granular threadwork. 
Fig. 12. The centrospheres do not lie upon exactly opposite sides of the nucleus. 
(This figure lay somewhat obliquely to the plane of the section, so that a con- 
