66 ■ EISEN. [Vol. XVII. 



of the cytoplasm. Frequently the plasmosphere is seen on 

 one side of the cell (Fig. 55), and not on the other, and it 

 seems that this is rather the rule than the exception. The con- 

 traction of the cell wall commences at the place where the 

 plasmospheric fragments touch the equator. Just previous to 

 this contraction the plasmosphere has at that point divided in 

 two in such a way that one-half of it lies immediately above 

 the equator, while the other half lies under it, that is, one-half 

 in each of the future daughter-cells (Figs. 55, 56), In the 

 mean time the mantle fibers have become connected by their 

 ends with the individual granules of the plasmospheric frag- 

 ments, the other ends of the fibers being attached to the 

 spindle pole. The contraction of the cell wall appears to be 

 accomplished directly by the contraction of the mantle fibers. 

 At a stage a little more advanced the ends of the mantle fibers, 

 which were at first attached to the spindle poles, become 

 attached to the cytoplasmic membrane around the nucleus 

 (Fig. 61). Another set of fibers have also made their appear- 

 ance in the vicinity of the mantle fibers. These fibers, for 

 which I propose the name of retractile fibers, connect the arch- 

 osome at the spindle pole, which has now passed through the 

 nucleus, with individual granules of the plasmosphere (Figs. 

 59-61), as well as with purely cytoplasmic granules along the 

 equator. While this contraction is taking place in the equator 

 of the old cell wall, a change has also appeared in the equator 

 of the central spindle. Instead of being comparatively dense 

 and even, larger and smaller vacuoles have formed (Figs. 56, 

 57). These vacuoles are at first diamond-shaped, with their 

 longer axis parallel to the spindle axis ; but later on they are 

 drawn out sideways, in the plane of the equator, while at the 

 same time plasmospheric granules appear along their mar- 

 gins. The new cell walls appear to be secreted out from these 

 granules along a double line of parallel walls of vacuoles. As 

 soon as the two parallel cell walls have formed they are sepa- 

 rated by the retractile fibers of the spindle cones. There are 

 thus four processes cooperating in the formation of the new 

 cell wall : the plasmospheric granules are placed along the 

 equator of the cell ; the central spindle is becoming vacuoled 



