TUE PROBLEM OP MITOSIS. 
569 
circular plate. According to this theory, which in principle 
resembles that of van Beneden, the astral rays are in a state 
of tension, their common insei’tion point being the centrosome, 
which plays a passive part in mitosis : on fission of the cen- 
trosome a new equilibrium is established by divergence of the 
poles and formation of a spindle between them ; and contrac- 
tion of the fibres causes not only divergence of daughter- 
chromosomes, but constriction of the cytoplasm itself. 
The contraction theory was further restricted in 1895 by 
Driiner, who denied contractility in the astral rays, and thus 
extended Hermann’s qualification to the entire achromatic 
figure. He affirmed, moreover, that the central spindle is not 
formed in the earliest stage, as Heidenhain, Hermann, Kosta- 
necki, and others believed, but arises later through union of 
astral rays of the two poles. Although his denial of con- 
tractility in the astral rays was not accepted by all investi- 
gators, Boveri, Flemming, Heidenhain, Kostanecki, and Meves 
adopted the view that centrosome divergence is caused by 
growth of the central spindle; and this explanation seemed to 
account for the contortion of these rays during the metaphase, 
and Recorded with infusorial mitoses in which centrosomes 
Avere said to be absent. In this and the following year R. 
HertAvig and Morgan independently produced asters in un- 
fertilised Echinoderm ova by chemical treatment; and 
Schaudinn described a neAv formation of centrosomes in the 
swarm spores of Acanthocystis. Furthermore Boveri con- 
cluded from the study of abnormal Echinoderm ova that 
spindle formation is uninfluenced by the nucleus, and that 
cell division not only depends upon both asters and spindle, 
but canuot occur in the absence of chromatin. 
The existence of elastic or contractile fibres was at this 
time denied by Gallardo, avIio formulated an electric inter- 
pretation of mitosis, assuming the centrosomes to be poles of 
opposite signs. This, hoAvever, Avas criticised by Meves, 
Avho said that crossing of rays is impossible in an electric 
field of unlike poles, and corroborated Driiner in restricting 
contractility to the mantle fibres. Rhumbler, on the other 
