No. I.] THE EGG OF UMAX AGRESTIC. 207 



at first pressed sideways against the upper pole (PI. XI, Fig, 7), 

 and as the polar globule is protruded, the rays are finally 

 massed together to form a " Zwischenkorper " (PI. XI, Fig. 8), 

 which for a long time marks the place of extrusion of the first 

 polar globule. The process of formation and extrusion of the 

 polar body requires nearly two minutes for its completion. 

 Soon after its separation from the Q.gg the first polar globule 

 collapses so that its position is marked only by a shriveled 

 membrane at the outer periphery of the egg. Mark has de- 

 scribed a similar behavior of the first polar globule in Limax 

 campestris. 



4. Formation of the Second Maturation Spindle. Extricsion of 

 the Second Polar Body. 



After the extrusion of the first polar globule the astro- 

 sphaere that remains in the egg undergoes a series of changes 

 that are shown in PI. XI, Figs. 10-14. The "cortical" and 

 "medullary" zones of the centrosphere become less sharply 

 defined as the sphaere continues to enlarge (PI. XI, Figs. 12 

 and 14). The astral rays, which often persist for some time 

 after the extrusion of the first polar globule, soon begin to 

 shorten as if by contraction, so that the centrosphere is seen 

 at one time surrounded by rays of uniform length, as in PL XI, 

 Fig. 12, and again by still shorter rays that terminate at their 

 inner ends at the periphery of the centrosphere, in a circle 

 of granular thickenings or "microsomes" (PI. XI, Fig. 13). 

 Within the circle of microsomes the rays are continued cen- 

 tripetally as extremely delicate fibers that extend through the 

 "cortical" zone to the "medullary" zone, which now appears 

 slightly granular. 



When the centrosphere reaches its maximum size it becomes 

 uniformly very finely reticular, so that it appears almost gran- 

 ular and at the same time loses its strong afifinity for staining 

 reagents (PI. XI, Fig. 14, a, b, c). In the center of the sphaere 

 the centrosomes are often distinguishable as two tiny, deeply 

 staining granules, as shown in PI. XI, Figs. 14 a and 14 r. 

 These centrosomes are evidently the same as those seen in the 



