THE METAPHASE. DIVISION OF THE CHROMOSOMES. 



25 



VI. THE METAPHASE. DIVISION OF THE CHROMOSOMES. 



Soon after the stage shown in Text-fig. XIV., the chromosomes become nearly straight and place themselves with 

 their lono- axis transverse to the long axis of the spindle. As they do so, each of them splits lengthwise into two exactly 

 similar halves, which are destined to pass to opposite poles of the spindle and enter into the formation of the two 

 respective daughter-nuclei. The two halves always begin to diverge first at that end of the chromosome turned towards 

 tiic interior of the spindle (Text-fig. XV.). From this point the halves seem to be pulled apart in opposite directions, 

 leavino- them still attached at the other end, at which point the final separation takes place (Text-fig. XVI. A). 



Fig. XV. 



Fig. XV. — Tlie metaphase. 

 AU of the chromosomes are spht lengthwise. The halves are being dragged apart at the inner end of the chromosome, but remain united by their outer ends. 



(Phototypes 2S, 29.) 



Plate VII. Phototvpe 28. 



Metaphase. Splitting of the Chromosomes {42 minutes) ; 1000 eiiamcters. 



This is the same specimen shown in Text-fig. XV. The spindle and asters are well shown — the centrospheres 

 slightly out of focus. The focus is sharply upon the chromosome at the upper edge of the spindle, which is clearly 

 shown in the shape of an inverted Y, the daughter-chromosomes being still united for about one-third their length. Two 

 similar chromosomes, not quite in focus, appear at the lower side, and one or two others near the centre. A more 

 enlarged view of the same equatorial plate is given in the following phototype. 



Pi.atf VIII. Phototype 29. 



'^Jie Same Specimen at an Enlargement of 3000 Diameters {focus slightly changed). 



In this figure most of the chromosomes shown in Text-fig. XV. can be individually made out (the illumination 

 employed was such as to sacrifice most of the detail in the achromatic structures). The splitting is clearly shown in the 



lower right-hand individual. 



