Lloyd Williams . — Studies in the Dictyotaceae . 
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EXPLANATION OF FIGURES IN PLATES IX AND X. 
Illustrating Mr. Lloyd Williams’ Studies in the Dictyotaceae. 
All the figures have been drawn with the aid of the camera lucida and the apochromatic 4.0 mm., 
aperture 1-30 of Zeiss with ocular 6 (x 800). For convenience of comparison the same scale 
of magnification has been kept throughout, but a few of the figures having been drawn from 
tangential sections are apparently smaller than they ought to have been. Figures 2-19 have the 
stalk-cell on the lower side, and the terms ‘ basal ’ and ‘ distal ’ are used with reference to this cell. 
Stalk- Cell Division. 
Fig. 1. Tetrasporangium rudiment before stalk-cell division. 
Fig. 2. Prophase of the stalk-cell division. The coarse spirem is beginning to segment and 
the nucleus is swollen and irregular in form. 
Fig. 3. Early spindle formation. One of three sections, slightly oblique, showing a number 
of curved, split chromosomes, the fragmenting nucleolus with its globule, and the basal pole with 
a few spindle-fibres. 
Fig. 4. Equatorial plate stage. The spindle is intranuclear. The remaining chromosomes are 
in another section. There is nucleolar globule on the spindle, and nucleolar fibrils between it and 
the membrane. 
Fig. 5. Anaphase stage. The two centrosomes are visible, but radiations are confined to the 
distal pole. The nucleolar globule is on the connecting fibres. 
Fig. 6. Telophase stage. The chromosomes form an irregular coil the strands of which in places 
appear double. The nucleolar globule is seen to the right. The tetraspore mother-cell nucleus 
is bigger than that of the stalk-cell, and its membrane is drawn out towards the distal centrosome. 
The First or Deduction Division in the Tetraspore Mother- Cell. 
Fig. 7. Early spirem. The nucleolus is vacuolated, and there are a number of small, deeply 
staining granules which probably fuse together to form the ‘ chromophilous spherule * peculiar 
to this mitosis. The radiations, to the right and left, are but faintly suggested, and no centro- 
somes can be distinguished. 
Fig. 8. The ‘knot’ or ‘Synapsis’ stage. The spirem is in two knots near the very faint 
centrospheres. The spherule is seen to the left. 
Fig. 9. Another example, showing the distortion of the nucleolus and the intimate connexion 
between it and the spirem. 
Fig. 10. A slightly later stage. The spirem is spread out on the basal side. A strand is shown 
attached to the nucleolus. The axis of the nucleus is not median but nearer the basal side. 
Fig. 11. The spirem is more evenly distributed over the membrane, and is distinctly beaded, 
with fine fluffy threads projecting laterally. The nucleolus has a large vacuole with included 
fibrils and granules. 
Fig. 12. The spirem begins to split in two, and the staining is less deep. The section is 
transverse to the nuclear axis. 
Fig. 13. A later stage in the splitting. The nucleolus and spherule appear in one of the other 
four sections through the nucleus. The reticulum becomes fainter. 
Fig. 14. The identity of the chromatin thread has been lost, and the nucleus appears as if 
in a state of rest. The spherule is still present. 
Fig. 15. A later stage. There are denser strands in the reticulum, the spherule has disappeared, 
the membrane, centrosomes, and radiations are more distinct, and the cytoplasm is differentiated 
into separate zones. 
Fig. 16. Early prophase. Thick cloudy bands appear, with indications of longitudinal splitting. 
The section is not median, and consequently does not include the nucleolus and centrosomes. 
Fig. 17. ( Taonia ). The chromosomes appear as loops with their limbs crossed, or as closed 
rings. The free ends of the chromosomes frequently appear split. The nucleolus is minutely 
vesicular. 
