MITOSIS (KARYOKINESIS) 23 



the chromosomes and become attached to them, one or 

 more sets from each pole being fastened to each chro- 

 mosome. In some way, perhaps by the contraction of 

 these fibrillae, the chromosomes are brought to lie at the 

 equator of the spindle, forming the so-called equatorial 

 plate. The chromosomes are of various shapes, like rods, 

 or resembling the letters J, V or U, more frequently the 

 last two. Usuallj^ the faint longitudinal split which 

 first became visible during the spirem stage is quite dis- 

 tinct. As the fibrillae attached to the chromosomes con- 

 tinue to contract the latter are torn in two along the line 

 of this longitudinal split, one half being dragged toward 

 each pole. When these daughter chromosomes, as they 

 are called, reach the two poles they soon join to each other 

 end to end and form spirem threads similar to those 

 formed before the cleavage into chromosomes (the di- 

 spirem stage). These elongate and finally form a long 

 tangled thread along which the chromatin begins to 

 assemble in lumps and which soon forms short lateral 

 connections to make the typical nuclear reticulum. In 

 the meantime the nuclear membrane has appeared 

 around each daughter nucleus and the nucleolus has made 

 its appearance. The kinoplasmic fibrillae around the 

 centrosome gradually disappear in the plants with cen- 

 trosomes, while in plants without centrosomes they dis- 

 appear in about the same way that they appeared, or in 

 the higher plants take part in the formation of the sepa- 

 rating membrane. In this latter case the spindle fibrUlae 

 seem to increase in number until they occupy the whole 

 width of the cell. At the equatorial plane a little knot 

 appears on each fibrilla. The fibrillae contract and as 

 they shorten the knots increase in size until by the con- 

 tact of the knots with each other a thin membrane (of 

 kinoplasm) is formed which separates the protoplasm of 



