580 
C. Jb'. U. MEEK. 
coucerning this problem : in the circumstances we must try 
to discover if any of these theories constitute an adequate 
explanation. 
We will fii’st deal with the arguments of Hartog. He says: 
‘^The absolute proof of the opposite polarity of the two 
centrosomes is to be found in the growth of the spindle by 
inflexion and coalescence of rays growing out from the 
centrosomes.” Now this can only mean that the mitotic 
spindle is formed by a force acting at two points, viz. its 
poles ; and that, since a known force cannot produce a 
spindle figure between two points if these points represent 
like poles, the mitotic spindle must be heteropolar if it is 
produced bj’" a known force. Let us assume that the spindle 
is formed in the manner described, and therefore that the con- 
clusion is valid. Now he says: “Since it is demonstrated that 
the cell-spindle is homopolar with respect to osmosis, 
currents, electrolytic or electrostatic force, magnetism is out 
of the question, (and) we may conclude that mitokinetism is a 
new force unknown so far outside the living cell.” By the 
first part of this sentence I understand that the mitotic 
spindle cannot be heteropolar with respect to known forces, 
because, if it is heteropolar, one point in certain mitotic 
figures must represent two poles of opposite signs — a 
reductio ad absurdum. By the second part I understand 
that, since it has already been shown that the spindle must 
be heteropolar if formed by known forces, such forces cannot 
be the cause of its existence; consequently we are dealing 
here with a new force. Let us consider this force. Now, if 
the spindle is formed as he believes by the action of this 
force at its poles, the last-named must be either unlike or 
like. We will assume the former. In this case certain 
mitotic figures cannot be explained unless we assume one pole 
to be of two opposite signs : and this is inconceivable. Let us 
now consider the alternative. In this case the new force is 
able to produce a spindle figure between two points at which 
it is given expression, when these points represent like poles. 
Hut this is contrary to fundamental principles of physical 
