948 
The Dual Force of the Dividing Cell. Part I: The Achromatic 
Spindle Figure Illustrated by Magnetic Chains of Force. 
By Marcus Hartoa, M.A., D.Sc., F.R.U.I. 
(From the Biological Laboratory of Queen’s College, Cork.) 
(Communicated by Sir W. Thiselton Dyer, F.R.S. Received December 1, 1904,— 
Read January 19, 1905.) 
[PuatEs 9—11.] 
I. 
Our first description of the polarised figure shown by the cytoplasm of the 
cell preparing for fission is due to Hermann Fol, who wrote in 1873: “ Auf 
beide Seiten dieser Kerniiberbleibsel zeigen sich Plasma-Anhiufungen, deren 
dicht angesammelten Kérnchen zwei regelmiassige sternformige Figuren 
darstellen.* Die Strahle dieser Sterne werden durch die in gerade Linien 
aneinander gereihten Kornchen gebildet. Mehrere solche Linien reichen von 
einem Stern oder Anziehungscentrum in einem Bogen zum andern. Das 
ganze Bild ist ausserst klar, und erinnert lebhaft an die Art und Weise 
ausgestreuter Eisenstaub sich um die beiden Polen eines Magneten anordnet 
Ich schliesse mich ganz und gar der Sachs’schen Theorie der 
Furchung durch Anziehungs-Mittelpunkte an, nicht etwa aus theoretischen 
Griinden, sondern weil ich diese Attractionscentren gesehen habe.” 
Thus the similarity of the cellular field to that of two unlike magnetic 
poles was recognised from the very outset. The figure in its highest develop- 
ment, as seen in Metazoa (figs. 1—5), has the character of a dumb-bell, whose 
spheroidal ends are termed “centrosomes,” and with the rays they give 
off, “ polar asters”; while the connection between them, of cytoplasmic fibres, 
is termed the “spindle.” The astral rays diverge through apparently 
undifferentiated cytoplasm ; but the spindle-fibres traverse or bound a clear 
space, apparently occupied by liquid during life. During the completion of 
the figure the nuclear wall has disappeared (fig. 1, EK); of its contents the 
rod-like bodies, known as chromosomes, are disposed in a symmetrical star 
across or around the equator of the spindle. The chromosomes now split 
(fig. 2, G): the respective sister-segments of all. diverge nearly simul- 
taneously, E, and glide to the centrosome (which they may even enter) and 
then fuse into the daughter nucleus (fig. 2, I,J), the same process taking 
place simultaneously at either pole. The present study is devoted to the 
bales Wey. os do 
+ “Die erste Entwicklung des Geryonideneies,” ‘ Jenaische Zeitschrift,’ vol. 7. 
