136 Historical and Critical Considerations 



assumes, in the region of the poles of the nucleus, a struc- 

 ture of parallel fibres. It soon becomes clear that we have 

 to do with the first signs of the spindle-fibres. These 

 develop quickly and continue through the interior of the 

 nuclear cavity, until they come into contact with each 

 other. There is no valid reason for the eventual assump- 

 tion that the spindle-fibres developing in the interior of 

 this cavity are of a different origin from the external 

 ones. On the aequator of the spindle the chromatic sub- 

 stance accumulates, touching the individual fibres at their 

 circumference. 



Next occurs the formation and longitudinal splitting 

 of the nuclear skein, followed by the separation and 

 moving apart of the two halves of the segments. Dur- 

 ing this period one sees clearly that not all the spindle- 

 fibres have succeeded in uniting with the opposite ones. 

 Only those that were successful in this are retained as 

 connecting fibres between the two young nuclei which 

 move apart. The space forming between them is sur- 

 rounded by a protoplasmic mantle toward the outside, 

 and apparently there collects in it a substance with osmotic 

 action which enlarges this space and drives the young 

 nuclei apart. In the meantime the number of the con- 

 necting fibres on the mantle of this space is lessened more 

 and more, the mantle itself is made to bulge more and 

 more in a transverse direction, and becomes correspond- 

 ingly thinner. Yet it remains sharply and plainly visible. 

 The space has assumed now the well-known barrel-shape, 

 its wall is called the connecting cylinder, and remains for 

 some time as an extended vesicle, closed in on all sides. 

 Finally, by being strongly distended in an aequatorial 

 direction, this vesicle reaches the protoplasmic accumu- 

 lation at the margin of the protruding dividing wall. It 



