﻿1903] BEHAVIOR OF THE CHROMOSOMES 259 



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manner similar to that of the first division. Attention was called 

 to the fact also that the spindle fibers may enter the nuclear cav- 

 ity before the spirem is completely segmented into the chromo- 

 somes, this being the case in both the pollen and embryo-sac 

 mother-cells, and my present studies have only confirmed this 

 statement. 



Gregoire claims that in Liliiim candidtun and L. spcciosum the 

 chromosomes become isolated and independent before the 

 nuclear membrane has disappeared. In some cases in Lilin?n 

 candidum diwd Fritillaria persicaiX. seems that the chromosomes are 

 isolated before the nuclear membrane disappears, but this is 

 rarely the case in Z. Martagon. Moreover, no special impor- 

 tance has been attributed to the fact that the spindle fibers enter 

 the nucleus in some cases before the individual chromosomes 

 are completely isolated. It is not necessary, however, to dem- 

 onstrate the identity of the chromosomes throughout the second 

 mitosis to show conclusively that two longitudinal divisions of 

 e chromatin occur during the first mitosis. 



After the nuclear membrane has disappeared and the multi- 

 polar spindle complex is laid down, or in the process of forma- 

 tion, the chromosomes are, as a rule, so closely entangled, kinked, 

 and twisted that it is impossible to trace them save in excep- 

 tional cases. For this reason it is extremely difificult, if not 

 impossible, to determine beyond all doubt the manner in which 

 they are formed from the spirem. Fig. 12 represents a section 

 of a daughter nucleus in the multipolar stage of the spindle. In 

 this case the spirem is more loosely arranged, and many of the 

 loops and turns may be traced with greater accuracy than in the 

 vast majority of instances. From this and figs. 13, 14, and ij, 

 It IS evident that the two segments of each chromosome in the 

 nuclear plate represent probably the two parallel limbs of the 

 loops observed at an earlier stage, which have become more or 

 less closely applied to and sometimes twisted upon each other. 

 The fact that the turns of the spirem in the daughter nucleus 

 are not all regular and uniform accounts for the twisted and 

 entangled condition of the chromosomes during the formation 

 of the spindle. In the mature spindle [figs. 14, t^) the chromo- 



