68 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



The completed bipolar spindle lies with its poles close 

 against the inner edge of the granular zone, which has as- 

 sumed an oval shape to accommodate itself to the outline of 

 the spindle. The spindle has sharply pointed ends (fig. 17). 

 It is composed of two sets of fibers. One set runs from pole 

 to pole forming the central spindle. The other runs only 

 from the poles to the chromosomes to which the fibers are 

 attached in bundles. These fibers contract and pull the 

 daughter chromosomes toward the poles. When this process 

 is completed the fibers of the central spindle no longer appear 

 straight but have assumed a wavy appearance. As the 

 daughter chromosomes approach the poles, the mantle fibers 

 appear (fig. 18). About this time the granular zone loses 

 its definite outline. It begins to break uj? in the plane of the 

 equatorial plate of the spindle and gathers about the poles 

 in two masses in which the daughter chromosomes lie em- 

 bedded. These two masses remain connected by a shell of 

 granular matter which outlines the old spindle. Figure 19 

 shows the beginning of this process and fig. 20 a later stage. 

 The cytoplasm seems to contain a greater quantity of gran- 

 ular matter than at any previous time. 



Within these two granular masses are formed the daughter 

 nuclei. These have at first a decided indentation on the 

 side toward the spindle (fig. 20). Later they become 

 spherical (fig. 21). The daughter nuclei are thus from the 

 first surrounded by a granular zone which, by the time they 

 are completely formed, has become relatively as wide and 

 as dense as that about the mother nucleus. The central 

 spindle fibers seem to disintegrate and when the nuclei are 

 ready for the second division remain simply as lines of 

 granules connecting the two granular zones (fig. 21). 



The second division, as far as could be observed, exactly 

 repeats the process of the first. It was impossible to follow, 

 under the dense granular zone, the elongating of the meshes 

 about the walls of the nuclei, but the concentric lines of 

 fibers were visible in many cases in the narrow space between 

 the zone and the wall. The breaking down of the nuclear 

 wall, the growing in of the fibers, and the formation of the 

 multipolar and bipolar spindles occur as in the first division. 



