272 Reed. — The Nature of the Double Spireme in Allium Cep a. 
more granular structure may be seen, but this does not stain with chromatin 
dyes. This reticulum appears to differ very little from the general 
cytoplasm of the cell (PL XVIII, Fig. 1). It is impossible to say (at this 
stage) whether the threadwork is a continuous structure or not, but 
subsequent events suggest that it is of the nature of a thin fenestrated 
sphere. 
One or more nucleoli may be present, and these are formed by sub- 
division in the hour-glass fashion described by Digby (1) for Galtonia. 
The first indications of approaching mitosis are seen in the nuclear 
reticulum. The chromatin begins to aggregate in small band-like masses 
on this framework, as shown in PI. XVIII, Fig. 2. It slowly spreads itself 
and builds up the spireme ribbon. It may have the granular structure of 
PI. XVIII, Figs. 3 and 4, or it may be fairly homogeneous, as in PI. XVIII, 
Figs. 5 and 6. Gregoire ( 7 ) maintains for Allium Cep a , and probably for all 
somatic nuclei, the existence of a discontinuous spireme. This point is 
extremely difficult of interpretation, for, when first formed, the spireme is 
a much-coiled structure, and the coils are often closely wrapped about the 
nucleolus (PI. XVIII, Figs. 6 and 7), but there appears to be little doubt 
that at this stage it is a continuous ribbon. The ribbon is coiled quite 
irregularly (PL XVIII, Figs. 6, 7, 8) within the nuclear vacuole ; no in- 
dication is seen of the arrangement into sixteen loops described by 
Schaffner (20). 
The nucleoli are intimately associated with the formation of the 
spireme. Even in the ‘resting’ stages (PL XVIII, Fig. 1) they may show 
fine fibrils of stainable matter radiating out to the nuclear reticulum. 
During the organization of the spireme these fibrils stain more densely 
(PL XVIII, Figs. 5 and 6), and there seems little doubt that substances are 
passing out from the nucleoli from which the chromatic spireme is built. 
When the chromatin band is fully formed, the nucleoli are left as faintly 
staining bodies, often vacuolated, and still later they may be seen extruded 
into the cytoplasm (Pl. XVIII, Fig. 16). No fragmentation of the nucleoli 
was seen as described by Digby ( 1 ) for Galtonia. 
Their ultimate fate was not followed, but it seems probable that they 
may become absorbed by the cytoplasm, for no trace of the core was ever 
seen in the cytoplasm of the daughter cell. 
During the ‘ resting ’ stages the nucleoli often contain regularly shaped, 
highly refracting bodies, as shown in PL XVIII, Fig. 1 a. Leitgeb ( 13 ) and 
Digby ( 1 ) have described these bodies in the cells of Galtonia candicans , 
&c. The latter observer suggests that these structures probably originate 
from the nucleolus. In the present instance there can be no doubt that this 
is the case, since they are actually situated within the nucleolus. Unlike 
the structures in Galtonia^ which stain with chromatin dyes, these in A. Cepa 
appear to be unstained. The structures are apparently absorbed during the 
