The individuality of the chromosomes and their serial arrangement, etc. 119 



As the fibres continue to push into the nuclear cavity the loops of the 

 spirem become flattened out in the plane of the equatorial plate. A 

 lateral view of this stage is shown in figure 13. This stage is a very fre- 

 quent one in my preparations. Figure 14 is a polar view of the series as 

 it enters the equatorial plate and it shows that the serial order of ar- 

 rangement of the chromosomes is still preserved. At this stage the spirem 

 is irregularly looped and its parts may be crossed. Later as the chromo- 

 somes come to lie in the plane of the equatorial plate, the entire spirem 

 lies in one plane without any apparent crossing of its parts. When the 

 equatorial plate is completely formed the chromosomes are rather closely 

 crowded together into an almost solid plate in which they are so evenly 

 spaced that the serial arrangement is not clearly in evidence. At this 

 time the nucleole is usually absent, but in some cases it can be seen at 

 one side of the plate, but much reduced in size (fig. 13). During the 

 late prophases the nucleole gradually decreases in size as if it were being 

 dissolved. 



It is to be noted that no split or line indicating the location of the 

 future plane of cleavage is to be seen in the chromosomes at any time 

 in the prophases. The mother chromosomes lie in the equatorial plate 

 as compact ellipsoidal masses forming a rather solid plate. The whole 

 number of mother chromosomes divides in the equatorial plate almost 

 simultaneously. In a lateral view of an early anaphase two rather even 

 ranks of daughter chromosomes are to be seen close together in the con- 

 dition shown in figure 15. The daughter chromosomes are ellipsoidal or 

 spherical in shape and when first formed they are about half the size 

 of a mother chromosome. 



A polar view of the group of daughter chromosomes during early 

 anaphase shows that the serial arrangement is probably still maintained 

 although the chromosomes are too close together to allow one to trace 

 with absolute certainty a continuous series for any considerable distance. 

 We may consider that in effect the discrete spirem that existed in the 

 equatorial plate has been split into two daughter spirems, and that the 

 chromosomes divide uniformly and simultaneously without losing their 

 serial order. The daughter chromosomes thus maintain the same serial 

 position with reference to each other which was occupied by the mother 

 chromosomes. As the poles are reached the daughter chromosomes are 

 usually closely packed together. Especially is this the case when a well 

 developed system of polar rays extends from the polar ends of the spindle 

 (fig. 16). In such cases the individual chromosomes are densely packed 

 together. When there are few astral rays the chromosomes are more 



