McAllister—Cytology and Embryology. 
637 
been frequently described and upon the breaking down of the 
nuclear membrane the double chromosomes seem to be pulled 
into the center of the nuclear cavity where for a short time they 
form a crowded mass in the center of the multipolar polyarch 
spindle. The chromosomes are then drawn out of the crowded 
central aggregation and form the equatorial plate. They at first 
become very much drawn out at the points of attachment of the 
spindle fibers as though considerable tension existed. This dis¬ 
tortion disappears as the spindle figure becomes diarch and at 
the time of the equatorial plate stage no traces of it can be 
seen (Figs. 26 and 27). 
As the chromosomes become arranged in the equatorial plate 
they have become shortened and thickened until their length is 
only about one and one-half times their diameter. In some 
chromosomes there seemed to be little or no difference in the two 
dimensions, the direction of the longitudinal segmentation be¬ 
ing the only index as to which was the longer axis (Fig. 28). 
There can be no question that the halves of the double 
chromosomes of the equatorial plate stage are the longitudinal 
halves of the spirem segments which were formed by the trans¬ 
verse segmentation of the spirem during the second contraction 
stage. The line of separation between the two halves of the 
heterotypic chromosome of the equatorial plate stage is the line 
of the first longitudinal segmentation of the spirem. This first 
longitudinal splitting which appeared before the second con¬ 
traction stage, has remained distinct throughout all the phases 
of second synapsis and diakinesis. At no time has there been 
any closing up of the first longitudinal split and a folding of 
parts of the spirem upon one another to form the double hetero¬ 
typic chromosome. 
The halves of the double chromosomes in the equatorial plate 
are drawn apart in the manner so frequently described, the 
ends toward the center of the plate separating first while the 
peripheral ends are last to separate. The smaller chromosomes 
of the interior of the plate usually are some distance from one 
another before the larger peripheral chromosomes are com¬ 
pletely separated. (Fig. 31). 
