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G. R. BISBY 
a slightly more advanced vState in that the cleavage furrows are of a 
greater diameter. Near the center of this figure cleavage has not 
actually been instituted, but the cytoplasm presents a more hyaline 
appearance, suggesting very clearly that cleavage in this place is 
about to result. 
In figure 9 is represented a stage of cleavage slightly more ad- 
vanced, in which the nuclei are in the equatorial plate stage of division, 
and each is surrounded by a hyaline space. The longitudinal view 
of the thread in this figure shows plainly its hollow nature. The 
manner in which cleavage furrows follow the threads is suggested by 
this figure, although it is difficult to picture the irregular fissures 
passing as they do at right angles to the axes of the capillitial threads, 
as well as up and down them. 
Figure 10 shows a still later stage in cleavage. The large piece of 
spore-plasm shown in the figure is bounded here and there by capillitial 
threads in close proximity. Many of the threads lie, in fact, in bays 
or deep indentations of the protoplasmic mass, suggesting their inti- 
mate association with the inauguration of the cleavage furrows. A 
shrunken lime knot is represented in cross-section at the upper left 
part of the figure. 
Figure 11, from a nearly mature sporangium, shows again the 
continuity of the inner portion of the sporangial wall and the exterior 
boundary of a larger lime knot, cut somewhat diagonally. The lime 
contents of both knot and wall have been largely removed by the action 
of the fixative. 
Figure 12 was drawn from a mature sporangium crushed in a drop 
of water on the slide. It shows a mature thread, plainly hollow and 
not solid, as might be supposed from a hasty examination, of somewhat 
varying diameter, and two lime knots, the larger of which is small 
compared with the size of an average knot. A spore is shown adjacent 
for comparison of size. Within the knot, as is in fact always the case 
in Physarella, are many granules of calcium carbonate, rather uniform 
in size and shape. When these are dissolved in acetic acid, the knot 
presents the same essential appearance as it does in sections of fixed 
material. 
Figure 13 represents a mature capillitial thread. As is shown, 
branching occurs; while the surface is smooth save for the "spines" 
occasionally present. This thread is hollow, as is represented in the 
figure, but this condition is by no means clearly apparent in every 
