22 



THE STRUCTURE OF CELLS 



fresh fibres are differentiated 'between the retreating groups of 

 halved chromosomes, and form the interzonal fibres (Verbindungs- 

 faden of the German writers). Whether these play any mechanical 

 part in forcing the daughter chromosomes apart is uncertain, as is 

 also the r61e assigned to the above-mentioned fibres that appear 

 to direct the chromosomes towards the poles. Probably the latter 



Fio. 10 (continued). 



Fucus vesiculosus, stages in the first mitosis in the fertilised egg (oospore). 7, Telophase. 

 (Phil. Trans, of the Royal Society.) 



are actively contractile, and there is some evidence to show that the 

 interzonal fibres are in a state of stress. In some instances, e.g. in 

 fertilised and segmenting eggs of Fucus, the arrangement of the 

 elongated plastids in this region plainly indicate such a condition of 

 stress or strain. But the achromatic apparatus varies considerably 

 in the degree of its complexity, and it probably would be unsafe to 

 attempt to assign constant functions to its constituent parts. So 

 much, however, may be said, that the chromosomes appear to be 



