238 LILLIE. [Vol. XVII. 



somes so that the inner sphere becomes a vesicle with deeply 

 staining wall and clear contents (PI. XXIV, Figs. 9, 11, and 

 12). The rays which were originally attached to the centro- 

 somes are now attached to the bounding membrane of the 

 inner sphere. Within the sphere are fibers attaching the cen- 

 trosomes to the wall, but independent of the radiations of the 

 aster. 



When the chromosomes are drawn up close to the inner 

 spheres (PI. XXIV, Figs. 11 and 12), the functions of the cen- 

 tral spindle and asters are for the time at least completed, and 

 both the latter become thickly studded with large microsomes. 



Then follows the outpushing of the first polar body 

 (PI. XXIV, Figs. 12, 13, and 14); as it is being formed, the 

 egg-sphere and chromosomes move up near to the periphery 

 of the Q%g, at the point of formation of the polar globule. 

 New rays are seen at this time extending from the central 

 sphere to the periphery of the Q.g% ; it is probably through the 

 activity of these that the sphere and chromosomes approach 

 the surface (PI. XXIV, Fig. 13), for the rays disappear as soon 

 as the chromosomes have reached their most peripheral position 

 (PI. XXIV, Fig. 14). This peripheral transfer of the sphere 

 and chromosomes results in the drawing out of the remains 

 of the original aster into fibers, as shown in PI. XXIV, Figs. 

 13 and 14. 



During the last phases of the formation of the first polar 

 body there is a very considerable diminution in size of the 

 sphere. This has the effect of bringing the centrosomes much 

 nearer together (Figs. 13 and 14). Sometimes, apparently, they 

 fuse ; or the process may go farther, and both centrosomes and 

 sphere may disappear. 



The mode of formation of the spindle of the second polar 

 body varies, according to whether the centrosomes and sphere 

 left over from the first division disappear or not. Let us con- 

 sider the latter case first. 



In this case there is within the &gg at the close of the first 

 maturation division the sixteen bivalent chromosomes, and a 

 sphere containing two compound centrosomes. This aggrega- 

 tion lies near the periphery of the egg. The aster that origi- 



