VITAL PKOI'HIi'TlKS OF CELLS 



are extremely difficult if not at present actually impossible. It may be 

 noted in passing also, tb.it the chromosomes are believed by many to be the 

 bearers of the determiners of hereditary characters a point to be further 

 discussed below. 



(2) Metapliase. This is a relatively brief stage in mitosis. It 

 includes the period when the chromosomes are arranged upon the spin<il>' 

 in the equatorial plate. Seen in polar view this is called the nintinxh'r 

 stage (Fig. 30, e). In this stage the chromosomes split longitudinally. 

 In dogtooth violet the number of chromosomes is twenty-four. A com- 

 mon form of chromosome is the U-shaped type. The point of attachment 

 to the spindle is the apex of the bent chromosome (Fig. 30, f). In the 

 more rapidly growing cells the double or split condition of the chromo- 

 somes has remained discernible since the preceding telophase, a true 

 resting stage having been omitted. At metaphase the already longi- 

 tudinally split chromosomes are completely divided, and the sepa- 

 rated moieties (daughter chromosomes) drawn toward opposite poles 

 (Fig. 30, g). 



(3) AnapJiase. The limits of this phase are indefinite (Fig. 30, 

 h to j). It may be said to include all stages between that when the 

 separation of the daughter chromosomes, resulting from the longitudi- 

 nally splitting of the mother chromosomes, is completely consummated, 

 and that when the groups of daughter chromosomes drawn to either pole 

 are still distinct. Seen in side or oblique view the later stages of this 

 phase present a double star arrangement of chromosomes hence 

 diaster stages (Fig. 30, i). The daughter chromosomes, an equal 

 number at either pole, were drawn apart by activity of the outer- 

 most of the spindle fibers (called man/It' fibers) presumably by process 

 of contraction. The inner or 'interzonal fibers' constitute the centra I 

 spindle. 



(4) Telopliase. Meanwhile a plate of granules (cell plate: mill- 

 body) has appeared in the equatorial region of the spindle. This marks 

 the plane of the future division (Fig. 30, j and k). In animal cells, an 

 annular constriction appears peripherally in the cell membrane. This 

 proceeds centrally throughout telophase until ultimately the mother-cell 

 is divided into two daughter-cells. The constriction of the cells in divi- 

 sion is generally interpreted as a phenomenon of alteration in surface 

 tension. Coincidently with the steps of this process, the chromosome- 

 and centrosomes (archoplasm material in plants) pass through the stages 

 of the prophase, but in inverse order : segmented spireme. loose spireme. 



