1903] STUDIES IN SPINDLE FORMATION 85 
that the kinoplasmic threads are nothing more than modified 
threads of cytoplasm, which have lost their reticulated and gran- 
ular character and have become more distinctly thread-like. 
fig. r shows one of the early stages in the formation of the 
weft, which ultimately develops into the spindle. Even in stages 
earlier than this, the fibrils were sharply differentiated, both in 
their structure and staining properties, from the surrounding 
cytoplasm. The fibrils gradually increase in numbers, evidently 
at the expense of the reticulum of the cytoplasm, and soon a 
fibrous zone of considerable thickness completely surrounds the 
nuclear membrane fig. 2. As far as the development of this 
zone-is concerned, the process is identical with that which occurs 
in Gladiolus (Lawson, 1900). In-Gladiolus, however, the chro- 
mosomes were already formed when the weft was developing, 
while in Iris the chromatin is yet in the spirem stage. 
fig. 2 shows the appearance of the fibrous zone when fully 
developed. Up to this time it increased in thickness almost uni- 
formly, but it now grows outward at irregular intervals. Two 
of these outward projections are shown in fig. 2. The meshes 
formed by the interlacing fibrils of the weft become elongated 
in the directions in which the fibrils are growing, that is, in the 
direction of the projection. These outgrowths of the fibrous 
zone are the first indications of the primary cones of the so-called 
multipolar stage of the spindle, and the threads composing them 
converge toward their apices. 
During the development of the cones the chromatin assumes 
the form of distinct chromosomes, and the nucleoli become 
vacuolated. 
The development of the cones is not only brought about by 
the pushing out of the original weft at certain intervals, but they 
apparently increase at the expense of the cytoplasm into which 
they project. Fig. 3 shows one of the cones projecting into the 
cytoplasm, and the outermost fibrils converging to its apex are 
continuous with the fibrils of the cytoplasmic reticulum. Fig. 4 
shows the cones at a later stage; the larger cone is much more 
Sharply defined. It has lost much of its reticulated appearance, 
and its fibrils are more independent of one another, except 
