192 
Mottier.—Dictyota dichotoma. 
siderable change of focus was necessary in drawing to include both centrospheres, 
and for this reason the centrosomes are a little nearer in the drawing than is really 
the case.) The spindle-cones, now well developed, have their bases turned toward 
the masses of chromatin and disorganized nucleolus; the polar radiations are few 
and indistinct. 
Fig. 13. The cones of fibres have formed a curved spindle; the nuclear mem¬ 
brane is still unbroken, except perhaps directly at the centrosomes. 
Fig. 14. A mature spindle with the same orientation of fibres; the chromo¬ 
somes, however, have fused into large masses. 
Fig. 15. A later stage, probably metakinesis. 
Fig. 16. A portion of a cell-plate (see text for further explanation). 
Figs. 17-22 pertain to nuclei of vegetative cells. 
Fig. 17. Nucleus of an epidermal cell not far from the growing point, in the 
resting stage; the centrosphere is present, but the kinoplasm occurs in smaller 
quantities than in reproductive cells. 
Fig. 18. Nucleus is prophase, showing chromatin spirem and large nucleolus. 
Fig. 19. Spindle with chromatin in equatorial plate; centrosomes very distinct, 
but no polar radiations; the entire nuclear membrane is present. 
Fig. 26. Similar to the preceding, but from a larger cell; the nuclear membrafie 
(not drawn) had partly disappeared. 
Fig. 21. Anaphase ; the chromosomes are crowded into a mass so that the limits 
of the individuals are scarcely recognizable; the centrosomes are smaller than at 
an earlier stage. 
Fig. 22. An epidermal cell of the thallus. The daughter nuclei are provided 
with membranes, and the centrosomes, with fewer radiations, are present; on 
either side of the region formerly occupied by the connecting fibres cell-plate 
rudiments are seen. The connecting fibres have been replaced by a network 
which stains as kinoplasm. 
Fig. 23. A germinating tetraspore. The centrospheres are on nearly opposite 
ends of the nucleus, which is structurally in the resting stage. The framework of 
the cytoplasm is more or less radially disposed about the nucleus. 
Fig. 24. Daughter nucleus, resulting from the first division in the tetraspore 
after cell-division is complete. The nucleus is in the resting stage, yet the centro¬ 
sphere shows that the karyokinetic activity of the next mitosis has begun. The 
persistence of the centrosome here is unquestionable. 
Fig. 25. A nucleus taken from an enlarging epidermal cell, which gave an 
indication of development into a tetrasporangium. 
