f 
' 
1906] MERRIMAN—NUCLEAR DIVISION IN ZYGNEMA 47 
ing-in process they come to lie in two closely adjoining parallel rows. 
As no case of a single row of isolated granules in the same plane was 
found, there is no evidence that such double row was produced by 
the division of a single row. Fig. 25 represents two rows of chromo- 
somes lying in the same plane. In fig. 12 fusion has taken place to 
such an extent that only three chromosomes are present in each row. 
Many of the chromosomes presented a tetrahedral appearance, - 
as in jigs. 16 and 20, thus pointing to the conclusion that the fusion 
of the condensing granules may take place in fours. In some cases 
the fusion has gone so far as to result in only four groups of tetrads 
(figs. 22, 23, 21). Fig. 24, of a more highly magnified group, shows 
especially distinctly this grouping of the granules. Careful focusing 
on this stage indicated the presence of another underlying group. 
As many cases were found of such grouping of the chromosomes in 
fours, it does not seem that it could have been purely accidental. 
When the maximum amount of fusion and condensation is reached, 
the limit apparently varying in different cells, each half of a group 
becomes dissociated from its adjoining members and gradually draws 
away, as in jig. 27. In process of separation each group becomes 
broken up into smaller groups, in the meantime all becoming again 
arranged in two rings concentric with the short axis of the cell (fig. 26). 
Thus numerous chromosomes are arranged in a circle in stages 
preceding and immediately following the stage of the equatorial plate, 
in which commonly four to six chromosome groups may be seen. 
It seems difficult to believe that six chromosomes (jig. 12) could have 
resulted directly from condensation and fusion of thirty or more 
chromosomes (fig. 14). A comparison of chromosomes as to size 
and staining qualities in the two adjoining cells (figs. 12, 13), drawn 
with Abbé camera, would certainly indicate that each chromosome 
must suffer a loss of its more liquid substance in the process of being 
drawn into the equatorial plate, or that a few must be entirely dis- 
solved. Whether all condense to form a few, or whether only a few 
are chosen to transmit the chromatin to daughter nuclei, the remain- 
der becoming dissolved in the cytoplasm, cannot be stated with 
certainty, as the staining process does not solve the problem as to 
the fate of the individual granules. When all the preparations are 
