i8 



INTRODUCTION. 



The daughter segments often diverge at one or at both ends (Fig. 8, 

 B, C). In other cases they may be bent and in contact only near the 

 middle (Fig. 8, D). If the daughter segments adhere at the ends, 

 and bend away from each other near the middle, a ring results 

 (Fig. 8, E). Ring-shaped chromosomes may be so bent as to bring 

 the opposite ends near each other, in which case we have a ring 

 partly folded upon itself. This is true in a measure in Fig. 8, E. 

 When the segments forming a ring separate slightly at one end, an 

 open ring is produced. 



A Y-shaped chromosome will result when the segments are con- 

 tiguous for a part of their length but diverge at one end (Fig. 8, F). 

 Sometimes the daughter segments adhere near the middle but diverge 



F 



FIG. 8. Heterotypic mitosis (Lilium ntartagon). Different forms of chromosomes. 

 A, B, C, D, chromosomes from prophase. E-K, from equatorial plate. 

 E, ring-shaped, F, Y-shaped, and J, typical X-shaped chromosomes. 

 G, H, I, and K, other forms commonly met with in Lilium. 



at both ends, so that they may be crossed ; this gives rise to the X- 

 shaped chromosome (Fig. 8, J). Instances are also met with in which 

 the segments of the X-shaped chromosome fuse completely at one end, 

 and the chromosome appears as a continuous rod, folded in such a man- 

 ner that the opposite ends are brought together. In this way loops and 

 incomplete rings are produced (Fig. 8, K). In Fig. 8, G, H, and I 

 are forms of chromosomes that are of frequent occurrence. The orien- 

 tation of the daughter segments toward each other, which results in the 

 different forms of chromosomes described, is, in all probability, of no 

 special importance, since two or more of these forms may be seen in 

 the same nucleus. 



In Tradescantia, between the time of the segmentation of the spirem 

 into chromosomes and the mature spindle, the daughter segments often 

 contract into the form of short, thick crescents. These may adhere at 



