388 K. MASUI: 
a few metaphase plates were observed. Each of the seventeen elements is 
univalent instead of bivalent, and often shows a longitudinal split. In those 
cells in which seventeen chromosomes are counted, one large chromosome 
usually appears which is quite similar in shape to the accessory chromosome 
of the first division (Fig. 76), and very likely is the same. 
Sometimes, as in the case of the horse, incomplete fusion of the chromo- 
somes is seen to occur, and in such a case occasionally nine or ten chromo- 
somes are found. From the appearance of the chromosomes, it is evident that 
their fusion in the second division is an incidental phenomenon. 
In the equator of this division each of the seventeen chromosomes 
becomes so placed that the line of the longitudinal split coincides with the 
equatorial plane and along this line all the chromosomes are divided at the 
same time (Figs. 77, 78). From this fact it is certain that the real character 
of the second division is simply an equation division, the accessory chromo- 
some being also divided into two, like the ordinary ones (Figs. 77, 78). The 
chromosomes in the anaphase and in the telophase are never fused but 
maintain their individuality (Figs. 79—82). 
The accessory chromosome :- In the beginning of the first division when 
the ordinary chromosomes become arranged at the equatorial plate, the 
accessory also lies for a while in the same plate with the ordinary ones 
(Fig. 66). In the polar view of the metaphase plate the accessory chromo- 
some can not with any certainty be distinguished from the ordinary, but in 
the later stage it is easily possible to make out this chromosome since its 
. behavior and its form are different from those of the ordinary ones. In the 
earlier metaphase, when the chromosomes assume short rod shape, all the 
cells contain seventeen chromosomes and in the side view of the same no 
special chromosome can be seen (Figs. 58, 66). In the later stage when the 
chromosomes begin to divide, assuming dumb-bell shape, the accessory passes 
undivided to one pole of the spindle in advance of the ordinary chromosomes 
(Figs. 68, 69). This shows that the accessory remains for a time in the 
metaphase plate. 
The accessory chromosome can be distinguished even at the late anaphase 
(Fig. 70), but in the telophase when the chromosomes collect so closely 
together that their individuality becomes entirely lost to view, the accessory 
