208 BYRNES. [Vol. XVI. 



archiamphiaster, but their form has changed. Between the 

 centrosomes a light region (the "centrodesmose " of Heiden- 

 hain) sometimes marks the position of the central spindle, but 

 at the time of the first appearance of the central spindle there 

 are no distinct fibers visible (PI. XI, Fig. 15). 



While still within the sphaere the centrosomes may become 

 surrounded by a distinct peripheral zone that stains less deeply 

 than the surrounding matrix. Sometimes no centrosomes are 

 visible within the centrosphere at this stage, as in PI. XI, 

 Fig. 12 ; they may, however, be present. Soon after their 

 separation the centrosomes in the centrosphere become the 

 focal points from which new astral rays diverge (PI. XI, 

 Fig. 16). At the same time the rapidly fading rays of the old 

 aster can be seen terminating in the peripheral ring of micro- 

 somes that surround the newly formed spindle. The rays of 

 the new asters elongate rapidly and reach far out into the cells, 

 so that at the equator of the spindle the rays from opposite 

 poles meet and cross one another.^ 



At first the chromatin lies entirely outside the newly formed 

 spindle, on the periphery of the centrosphere, where it was 

 left after the extrusion of the first polar body. In the interval 

 between the extrusion of the first and second polar globules no 

 nuclear membrane is formed. These relations are shown in 

 PI. XI, Figs. II, 14, and 15. As the second maturation 

 spindle enlarges and the sphaere in which it is first formed 

 fades away, the chromatin comes to lie on the upper surface of 

 the central spindle, which at first forms at right angles to the 

 polar axis of the egg. Finally the chromatin is drawn into the 

 equator of the spindle, where it forms the equatorial plate. As 

 the poles still continue to separate, the spindle sinks into the 

 Qgg and rotates through an angle of 90 degrees. After it has 

 reached its maximum growth (PI. XI, Fig. 19), the second 

 maturation spindle comes to rest at the upper pole of the egg. 

 It is worthy of note, in the Qgg of Limax, that during the forma- 



^ This account of the formation of the rays of the second maturation spindle 

 differs from Mead's account of the formation of the aster in the second maturation 

 spindle in Chaetopterus, where the rays of the old aster are merely focussed on 

 new centrosomes. 



