THE DIVIDING CELL 



345 



corpuscle of a mammal ; whereas in the cell, as in the " false 

 spindles," the poles themselves diverge during the process of 

 mitosis. Clearly the fact is, the separation of the centrosomes 

 during the growth of the spindle cannot be referred to our 

 dual " mitokinetic " force, and we must seek another explanation. 

 The bulging of the spindle-figure in the endosperm of flowering 

 plants and other facts indicate that the outer zone of the spindle 

 is a continuous membrane, semi-permeable to liquid, and that 

 the cavity through which the spindle-threads run is turgescent ; 

 this is certainly one factor in the character of the growth of the 

 spindle, and in the separation of the centrosomes. Moreover, 

 the outer cytoplasm must also exert a tractive influence, pulling 

 the centrosomes towards the periphery of the cell. We have 



Fig. io. 



direct evidence of this in many of the cell-figures of the embryo 

 of Rhynchelmis (fig. io). Here the centrosomes are elongated by 

 this pull and drawn out into doublets or " blobbed," the smaller 

 blob being next the spindle, as if that part anchored by the pull 

 of the spindle fibres had resisted the pull of the outer cytoplasm 

 more than the section in direct contact with the cytoplasm. 



The irregular distribution of the polar rays in Rhynchelmis 

 points to the existence of cytoplasmic creep, which disturbs their 

 distribution. Just so do currents deviate the magnetic chains 

 in a glycerine field. The well-known spiral asters or polar 

 fields in the segmenting egg of the slug (Limax) afford a still more 

 striking proof of the activity of the outer cytoplasm during 

 mitosis. Thus, far from referring all the complex of forces 



