March, 1908.] On the Cytology of Synchytrium. 
281 
trosomes. This is particularly true of the stage represented by 
fig. 14, where the chromatin is in spirem in every one of the nuclei 
in the three cysts observed although the aster has apparently run 
its course. This suggests that we have not reached a full under¬ 
standing of the phenomena as yet. Nevertheless in any case it 
seems certain that the resting nucleus, with its chromatin all or 
nearly all eoncemrated in the single globular karyosome (figs. 
12-13) must be connected-with the chromosomes of anaphase 
bv a series of stages not far divergent from these here described. 
The cycle of astral activity which is the main interest of the 
present paper may now be taken up. When at their maximum 
size the rays are relatively few, long, and so thick as to be 
clearly visible under a low magnification. They are not always 
straight (fig. 7) and do not always center exactly in the focus 
of the aster (fig. 12). Quite often they have thickenings or 
granules along their length (figs. 2, 4, 5, 12). These are apt 
to be located at the intersections of the rays with the strands 
of the cytoreticulum (fig. 5). At later stages the central 
deep staining granule gives place to a larger diffuse gran¬ 
ular area in which there may be still some deeper staining granules 
but they are more minute than those which preceeded them. 
The rays at the same time become finer and moi'e numerous till 
they resemble the spindle fibres in ordinary mitosis. The granu¬ 
lar area then appears to enlarge while the rays disappear and 
finally the centrosome seems to become simply a densely granu¬ 
lar mass of cytoplasm which does not stain more deeply than the 
general reticulum (fig. 14). In this stage the centrosome re¬ 
sembles greatly the so-called attraction spheres of some animal 
cells, e. g., some stages of Ascaris. This mass is then dissipated 
into the general cytoplasm by imperceptable stages thus leaving 
the nucleus without centrosomes as it began. As before indicated 
the condition of the nucleus at this time throws some doubt upon 
this sequence so that the history of the centrosome, like that of 
the nucleus, may be subject to some revision. But it appears sure 
that the centrosome arises de novo out of the cytoplasm and dis¬ 
integrates into cytoplasm again whether the sequence of events 
be exactly that given or not. 
The remarkable feature of the aster, however, is the relation 
of the rays of the centrosome to the reconstruction of the nucleus. 
At an early stage a vacuole appears around the chromosomes. 
This is at first quite without a membrane (fig. 2) but verv soon 
those astral rays which are nearby come to form a cone enclosing 
it (figs. 3, 4). Soon the ends of the rays bend around the vacuole 
and enclose it forming the nuclear membrane (figs. 5, 6, 7). These 
membrane-forming rays may be observed to taper greatly from 
the center toward the curved ends (figs. 4, 7). At their thicker 
ends they are very heavy indeed and stain deeply so that they 
