594 GRIFFIN. [Vol. XV. 



nuclear membrane, their rays are approximately similar in struc- 

 ture. As soon, however, as the chromosomes enter, in any 

 considerable extent, into the system, certain rays commence to 

 stand out more prominently. They are thicker, more deeply 

 staining, than the remaining rays, and more homogeneous in 

 that they are not microsomal in structure. As they can be 

 traced to the chromosomes, they are evidently the developing 

 traction-fibers (" Zugfasern ") and are to be regarded as devel- 

 oping out of rays at first identical with the astral rays (cf. 

 Drliner, '94). In both maturation-spindles these fibers stand 

 out prominently, and in structure convey the impression as of 

 threads spun of numerous strands. But a single traction-fiber 

 is attached to each daughter-chromosome (PI. XXXI, Fig. 12), 

 as has been described by so many other observers in other 

 forms. 



Besides those attached to the chromosomes, the spindle con- 

 tains numerous other fine and light staining fibers, which in 

 some cases can be traced continuously from pole to pole. As 

 there is here no distinction between central spindle and mantle 

 fibers, these central spindle-fibers occur scattered throughout 

 the entire spindle. In equatorial section they can be seen as 

 numerous dots among which the chromosomes of the solid equa- 

 torial plate are interrupted. 



Movements of the Polar Amphiasier. — In the stages previous 

 to completion of the spindle, the line joining the centrosomes is 

 very seldom situated in an egg radius. The completed spindle 

 is, however, radial in position, with its aster still quite distant 

 from the surface of the egg. It must, therefore, have under- 

 gone some rotation or change of position, however slight. 

 Owing to absence of all means of orienting the spindle with 

 reference to a fixed point of the egg, it was impossible to 

 determine the precise extent of this shifting, though the occur- 

 rence of sections in which the spindle is oblique to the egg 

 surface proves conclusively that it rotates to some extent. 

 Sections through either aster of the just completed spindle 

 show how completely the discarded nuclear skein has become 

 involved in the astral system. The rays then appear to be but 

 rearranged strands, the granules serving as microsomata (PI. 



