4 INTRODUCTION. 
tance. Near the nucleus the cytoplasm is more granular, with smaller 
meshes. It is more nearly a thread-like net-work than alveolar in 
structure, and appears with differential staining as kinoplasm. This 
very fine granular thread-work often extends in among the radiations 
of the centrosphere. 
The resting nucleus shows a large vacuolated nucleolus and a fine 
linin-reticulum with rather large meshes, upon which are arranged 
small and nearly uniform granules, all of which do not react as 
chromatin. With the advance of karyokinesis, the chromatin begins 
to collect into larger and somewhat irregular masses that finally become 
the chromosomes. There is not developed, as in vegetative cells of 
this plant, a regular and uniform chromatin spirem or ribbon. The 
nucleolus becomes more vacuolated and soon disappears. The nuclear 
cavity presents a more granular appearance, the granules staining 
more densely. 
The kinoplasmic fibers now penetrate the membrane of the nucleus 
and enter its cavity, while at the same time the polar radiations seem 
to diminish in number (Fig. 1, C). On entering the cavity some of 
the fibers proceed in advance of the others. Some pass straight to- 
ward the center of the nucleus, while others diverge toward the sides. 
As these fibers approach from opposite sides of the nucleus, they tend 
to collect the chromosomes into an irregular mass in the equatorial 
region, where they finally form the nuclear plate (Fig. 1, D). Cer- 
tain of these fibers coming from opposite sides seem to unite at their 
ends to form the continuous spindle fibers which extend from pole to 
pole; others fasten themselves to the chromosomes, and still others 
diverge toward the nuclear membrane in the equatorial region (Fig. 2, 
E). In the mature spindle, therefore, the fibers present the following 
orientation: those radiating from the poles, the continuous spindle 
fibers extending uninterruptedly from pole to pole, those running from 
the poles to the chromosomes, and the fibers which diverge from the 
poles toward the equatorial region and end in the cytoplasm (Fig. 2, F). 
The nuclear membrane in the tetraspore mother-cell of Dictyota 
disappears very gradually during the process of karyokinesis, often 
persisting at the sides when the spindle is mature (Fig. 2, F). It begins 
to disappear at the poles as soon as the fibers enter the nuclear cavity, 
and by the time the anaphase is reached no part of the membrane can 
be distinctly seen. Thus the spindle, with the exception of the polar 
radiations, lies within the nuclear cavity, its fibers, however, being 
largely of cytoplasmic origin, To what extent any nuclear substance 
contributes to the formation of the spindle is difficult to determine. 
On the disappearance of the nucleolus, numerous granules appear in 
