1913] MERRIMAN—SPIROGYRA 327 
terial is seen to assemble more at the ends of the double V’s, thus 
presenting the appearance of tetrads (fig. 28). The V-shaped 
chromosomes represent but the loops or portion of the loops of 
the original spireme now ruptured. Each V has the characteristic 
line as seen in the original spireme, showing it to consist of parallel 
threads of chromatin. The more deeply stained ends of the loop 
are homologous with the structures described by BERGHs (1) as 
the true chromosomes reappearing from the mass of “‘pseudo- 
chromosomes,” an interpretation which seems unwarranted when 
their whole history is taken into consideration. 
After rupture of the spireme, the chromosomes do not form 
daughter spiremes, but joined by anastomosing bridges of linin 
cohere loosely in a ring or disk (fig. 32, 33). These figures are not 
dissimilar to those of GREGOIRE (8) in Trillium, where each of 
anastomosed chromosomes after polar assemblage becomes by | 
alveolization an elementary reseau, at once of an alveolar and 
reticular nature. The chromosomes in the ring or disk gradually 
shorten their loops, and approach each other more closely until a con- 
fluence of the chromatic material results in one to several vesicular 
masses (figs. 35, 36) lying within a granular material that formerly 
was at the ends of the spindle and into which the chromatin re- 
treated. These masses are crossed by cavities, spherical or poly- 
hedral. At this time the chromatic masses are surrounded by a 
clear Space, around the margin of which the nuclear membrane 
begins to evolve (fig. 37). 
Summary 
A summary of the results obtained that differ most from others 
published is as follows: 
se Spireme originates from material derived from both nucleolus 
nuclear network. The materials constituting this spireme are 
aggregations varying in appearance, in number, and in staining 
Capacities. 
These aggregations are not the chromosomes. They greatly 
e i . 
See im number that published for chromosomes in any species 
Pirogyra; although a comparative study of plates of other 
