266 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 30 Ser. 



but gradually become displaced. The fibres increase in 

 number and soon begin to attach themselves here and 

 there to the chromosomes, at first singly, and later in bun- 

 dles; the latter condition is shown in fig. 13. The fibres 

 now begin to take on a parallel arrangement, and the cones 

 separate into two groups marking the beginning of the 

 fascicular stage. It may be remarked, in passing, that the 

 condition shown in fig. 12, where two of the cones seem to 

 dominate the rest, and the fibres stretched between them 

 tend to be parallel, is but temporary. 



4. Fascicular Stage. 



The fascicular stage is characterized by the increase in 

 number of the cones, as is clearly seen in fig. 15. This is 

 the result of a rearrangement of the fibres, whereby each 

 cone becomes broken up into several. In the meantime 

 the arrangement of the fibres becomes more parallel, and 

 the chromosomes collect in the region of the equator (figs. 

 14 and 15); at the same time the mantle fibres begin to 

 develop. 



5. Bipolar Stage. 



The transition to the bipolar stage is easy to follow in the 

 preparations ; the cones gradually fuse until the stage shown 

 in fig. 16 is reached. This, as will be seen in the figure, is 

 not strictly bipolar, but the ends of the spindle are drawn 

 out into two or more long points which often extend to the 

 limiting membrane. In many spindles the fusion is com- 

 plete at one or both of the poles, so as to form a sharp point ; 

 but a large proportion of them remains even during the 

 anaphase, in the condition shown in fig. 16. 



During the stellar and fascicular stages the cytoplasm 

 loses almost all trace of its radial arrangement; there is a 

 layer of less dense cytoplasm around the spindle (figs. 

 10-16). 



The completed spindle presents in surface view the 

 appearance shown in fig. 16; there is little or no trace 

 of connecting fibres; in median optical section, however, 



