No. I.] THE EGG OF UMAX AGRESTIS. 209 



tion and rotation of the second polar spindle the astral rays 

 are always straight. There is not the slightest indication of a 

 spiral arrangement of the aster, so that mere migration of the 

 spindle cannot explain the spiral twisting of the astral rays 

 that follows later. The centrospheres of the second polar 

 spindle are very similar to the second stage of those already 

 described for the first polar spindle; compare PI. XI, Figs. 19 

 and 8, and Figs. 20 and 7. The centrosphere contains a 

 deeply staining center, surrounded by a less deeply staining 

 peripheral zone from which the astral rays diverge ; no definite 

 central granule is distinguishable. The centrosphere may en- 

 large, but it always retains this general character throughout 

 the stage of the second maturation spindle, and never develops 

 the sharply marked zones that are characteristic of the archi- 

 amphiaster stage. 



Notwithstanding the similarity that often exists between the 

 first and second maturation spindles, they can always be identi- 

 fied by the presence of peculiar deeply staining bodies that 

 group themselves around the equator of the second spindle. 

 Only one of these bodies is represented in PI. XI, Fig. 19, but 

 there are many similar structures in the Q.g^. They are more 

 or less regular in outline, being round or slightly oval, but they 

 are apparently without any definite structure. In the earlier 

 stages they are sometimes present as vague bodies lying around 

 the periphery of the Q^^, but just before the extrusion of the 

 second polar globule they tend to aggregate around the spindle 

 in the upper hemisphere. These bodies probably owe their 

 origin to the circular rings in the ovarian eggs, and are no doubt 

 to be regarded as the yolk-nuclei of various authors. 



There is no apparent difference in the size of the two 

 astrosphaeres of the second polar spindle. The distal aster 

 presses close against the periphery of the ^gg, which again 

 becomes slightly flattened just before the extrusion of the 

 second polar globule. The time required for the formation and 

 separation of the second polar globule is about two minutes — 

 the same as that required for the formation and extrusion of the 

 first. After the second polar globule has been extruded, 

 the egg-nucleus immediately forms a membrane and becomes 



