28 INTRODUCTION. 
fastened to the fibers either at the free ends or at the place of bending. 
Now, in order that the two segments of such a chromosome may come 
into contact side by side, as is frequently the case, the parallel parts of 
the loop need only be brought closely together. This may happen 
Fic. 11.—Second, or homotypic mitosis, in pollen mother-cells (Lz/zumz). 
A, multipolar stage of spindle; chromatin spirem not completely segmented into chromosomes, 
B, bipolarity established ; chromosomes more regularly arranged. 
C, mature spindle ; chromosomes more regularly disposed in equator, placed radially or tangentially 
on spindle. 
D, metakinesis. E, the anaphase. 
before the spirem is completely segmented, for in many chromosomes 
the two segments are very closely applied and twisted upon each other 
before the spindle is mature. In like manner parallel portions of the 
spirem may come in contact either before or after segmentation. In 
many other cases, both in the mature spindle and during its develop- 
