The life history of Diplodiscus temporatns Stafford. 627 



In a side view of a nucleus which seems to be in a stage 

 slightly earlier than the last figured, the chromosomes appear massed 

 together while they are evidently being arranged to form the 

 equatorial plate. In the metaphase the chromosomes have lost their 

 connecting fibres, so that each one is distinct from all the others 

 (Fig. 26). 



Fig. 27 and 28 represent later stages in the formation of the 

 chromosomes and their arrangement about the middle of the spindle 

 to form the equatorial plate. In these figures it will be seen that 

 the centrosomes are very prominent. They are comparatively large 

 and stain, with the haematoxylin , practically as deeply as the 

 chromosomes. 



In Fig. 26, which represents a section through the equatorial 

 plate of a nucleus in the metaphase of mitosis, the chromosomes are 

 seen to be arranged throughout the greater part of the area of the 

 nucleus. In other sections they were found in a ring about the 

 periphery of the nucleus, so there is no constancy in their 

 arrangement. 



In such a section, at right angles to the spindle, the chromo- 

 somes are usually somewhat dumb bell-shaped, and of practicallj^ 

 equal size. In all cases where the section is cut in such a manner 

 as to show the entire number of chromosomes, there are found to 

 be sixteen. In especially favorable side views of the mitotic figure, 

 befoi'e the splitting of the chromosomes, this count can be verified 

 (Fig. 28). 



In side views the shape of the chromosomes is elliptical, their 

 diameter being about one half their length. At no time in the 

 mitosis do the chromosomes assume the long filamentous shape such 

 as has been figured by Goldschmidt (1905) for the chromosomes 

 in the egg from the hermaphroditic generation of one of the 

 Heterocotylea {Polystomum). 



In the figure last mentioned, as well as in all figures of side 

 views of the mitotic figure, the prominence of the achromatic figure 

 is well shown. In reality the linin fibres are much stouter than 

 they are shown in any of the figures. They are represented hy 

 thin lines only on account of the method by which the drawings 

 were made. If thej- had been drawn to scale they would, in a 

 black and white figure, be nearly as prominent as the chromosomes. 

 Each of the spindle fibres is made up of a number of elements. 

 There were most commonly four of these elements in each fibre. 



