THE CELL AND CELL DIVISION 



53 



chromosome into two parallel halves. This forms two equal 

 and similar groups of daughter chromosomes, each group 

 similar to the original group except in size. As a matter of 

 fact this longitudinal splitting of the chromosomes is by no 

 means always deferred until this time, for frequently it occurs 

 during the pro phase of division, even in the spireme stage; or 

 rarely the chromatin granules may divide even before a definite 

 spireme is constituted (Fig. 23) . In such cases the chromosomes 

 are in the form of double rods throughout the entire prophase 

 and mesophase; the metaphase is then present only virtually. 



The mantle fibers from the oppo- 

 site poles of the spindle are now 

 attached to the daughter chromo- 

 somes, usually in their middles. 

 Next the mantle fibers begin to 

 shorten as the result of some proc- 

 ess centering in or about the cen- 

 trosomes at the poles of the spindle. 

 As the poles are relatively fixed, 

 perhaps by the anchoring asters or 

 through the rigidity of the central 

 part of the spindle, the result is the FIG 23 ._ Longitudinal fission 



Separation Of the tWO groups Of of the spireme in the division of 

 j i, -i v v spore-mot her-cell in Lilium can- 



daugnter Chromosomes Which move didum. After Farmer and Moore. 



along the central spindle fibers to- 

 ward the regions of the centrosomes. If the mantle fibers 

 are attached to the middle of the chromosome it is first 

 drawn out into a 3- or > -shape; frequently this form is 

 assumed during the mesophase, the apex of the > pointing 

 centrally in the equatorial plate (Figs. 20, F, H; 21). The 

 period of mitosis occupied by the divergence of the two chro- 

 mosome groups is called the anaphase; this is usually very brief 

 as the chromosomes diverge rapidly. Their divergence exposes 

 the central fibers of the spindle which are then called the 

 interzonal or connecting fibers, and which frequently come to 

 have an important share in the formation of later structures 

 (Figs. 21, H; 22, E). In their divergence the chromosomes 



