182 W. WALDEYER. 
Strasburger, and Mayzel, we are still in doubt as to the origin 
and meaning of the spindle figure and polar rays; nor do we 
know anything definite as to the ultimate fate of either of these 
structures. But unquestionably the “nuclear spindle ” is one 
of the most important phenomena in karyokinesis, and I do not 
think I shall be mistaken if I anticipate further advance in 
our knowledge of the nature of mitotic division from the 
elucidation of the origin and fate of the spindle-threads. 
If we exclude the isolated statement (already mentioned) that 
the nucleoli take a share in the formation of the spindle 
figure, there are at the present time three views as to its 
origin :—(1) The achromatic threads arise chiefly from the 
cell-protoplasm (Strasburger, Guignard, and others, chiefly 
botanists) ; (2) they arise from the achromatic thread 
substance of the nucleus (Biitschli, Flemming, Pfitzner, 
Carnoy, Rabl, O. Zacharias, and Schewiakoff) ; (3) they arise 
both from the achromatic nuclear constituents, and 
from the cell-protoplasm (E. van Beneden, Heuser, Plat- 
ner, and others). With regard to Platner’s view it should be 
remarked that in Arion (160) it is, according to him, formed 
only from the achromatic nuclear constituents. In a second 
contribution, however (161), he derives the polar part of the 
threads from the cell-protoplasm, and the equatorial part from 
the nuclear substance. He agrees in this with H. van Beneden, 
who holds the opinion (23, 24) that at first the two halves of the 
spindle figure are separated at the equator, so that instead of 
spindle-threads we have two cones. This agrees with Boveri’s 
account of Ascaris megalocephala (34), whereas Flemming 
(68) asserts that this condition has no claim to generality. 
Boveri’s view (84) sounds peculiar and contradictory, viz. that 
the spindle-threads in the formation of the so-called “ directive 
bodies ” (see below) arise from the achromatic nuclear consti- 
tuents, but that during the segmentation of the egg-cell they 
arise from the cell-protoplasm (Ascaris megalocephala). 
Strasburger (191) recognises that in Spirogyra poly- 
teeniata the greater part of the spindle figure is formed from 
the cell-protoplasm, and in agreement with van Beneden’s 
