56 CENTROSOMES, SPINDLE AND ASTERS [CH. 



plane farthest removed from the influence of the centro- 

 somes 1 . Several investigators have supposed that cell- 

 division is determined by surface tension, and that division 

 takes place along a zone where the surface tension is reduced. 

 If, then, for any reason the zone of the cell farthest from the 

 centrosomes has a lower surface tension than elsewhere, this 

 would be in accord with all the facts, for in a typical 

 dividing cell the plane of the equator of the spindle is that 

 farthest removed from the centrosomes. 



This conclusion is supported by TEICHM ANN'S rule of the 

 relation between size of mitotic spindle and formation of 

 division furrows, quoted in the preceding chapter. The 

 rule states that the rate of formation of the cytoplasmic 

 furrow varies with the length of the spindle and with its 

 nearness to the surface of the cell, and if the amount of 

 reduction of -surface tension varies with the distance from 

 the centrosome, evidently it would be relatively greater the 

 longer the spindle and the nearer the spindle to the egg- 

 surface. Or, otherwise expressed, if the surface tension of 

 the cell surface is greatest in the region nearest the centro- 

 somes and least in the region farthest away from them, the 

 greatest possible difference will be produced by having the 

 longest possible spindle lying parallel with the surface and 

 as near it as possible. 



The greater part of the experimental and observational 

 evidence thus suggests that cell-division is ultimately 

 dependent rather on the mitotic figure, and probably more 

 especially in the position of the centrosomes, than on tii 

 division of the nucleus which normally precedes it. 

 fact, however, is not at first sight quite easy to recon^gc 



1 That the centrosomes do exert some kind of "influence at a distance" 

 is indicated by the fact that in the synapsis (synizesis) stage of developing 

 germ cells (see Chapter V) the spireme is crowded towards the side of the 

 nucleus nearest to the centrosome, and HARDY has produced similar figures in 

 resting nuclei by subjecting them to an electric current (1913). 



