22 INTRODUCTION. 



or it may have had this form at an earlier stage. The chromosome at 

 the right in this figure (Fig. 9, C), was attached to the spindle end- 

 wise, and the retreating granddaughter segments will probably form 

 Vs. If the chromosome on the left were rotated 45, so that the seg- 

 ments would be seen in profile, we might have the picture of two 

 double V's or U's about to separate, for, as shown in the figure, the 

 free ends of the pairs of granddaughter elements tend sometimes to 

 diverge. The two chromosomes in this figure, which belong to the 

 same spindle, show clearly how figures of the same shape may be pro- 

 duced in different ways. In the one on the right the chromosome was 

 probably attached to the spindle by the end, and the V's are formed by 

 the divergence of the free ends, while that on the left was fastened near 

 the middle of each segment, and the V- or U -shape of the retreating 

 segments is the result of a bending. 



In such chromosomes as Fig. 8, G, H, I, the retreating elements 

 may retain their present form, or they may be bent during metakinesis 

 into U's or V's. When the daughter segments of such chromosomes 

 are separated, they must untwist, and it is reasonable to suppose that 

 the force necessary to separate them when twisted will be sufficient to 

 bend the segments into a U- or V-like figure. 



THE ANAPHASE. 



The pairs of granddaughter segments, as they pass toward the poles, 

 are in the form of contiguous, straight, or undulating rods, V's or U's, 

 or, in case one limb of the last two named figures be much longer 

 than the other, as is sometimes observed, the retreating elements will 

 be in the form of hooks. Even in those cases in which both grand- 

 daughter segments are nearly straight or undulating rods of equal 

 length, each is often slightly bent or hooked at the end fastened to the 

 spindle fibers, or the segments may be bent at both ends. 



The daughter chromosomes in Podophyllum and Tradescantia 

 show with great clearness their double character during the anaphase 

 (Fig. 9, E). The granddaughter segments generally lie close side by 

 side, although cases in which they are slightly separated are now and 

 then to be observed. There are in these genera also variations in the 

 forms of the chromosomes which may be explained in the same man- 

 ner as in Lilium. 



The retreating chromosomes and the structure of the spindle suggest 

 that the segments are conveyed to the poles by a pushing and pulling 

 action of the spindle fibers. 



