150 Wilson. — On Spore Formation and Nuclear 
them to the chromosomes. At this stage the longitudinal fission was again 
seen in the individual chromosomes (Fig. 25). These become arranged near 
the periphery of the nucleus, but the final stages of diakinesis were not 
observed. 
Up to this time no sign of spindle formation is to be seen, but a little 
later the fibres become evident in the cytoplasm. These are directed 
towards the two bluntly-pointed poles ; as in the premeiotic divisions no 
polar radiations or centrosomes were found. The nuclear membrane has now 
disappeared and the chromosomes lie free near the centre of the cell (Fig. 26). 
The nucleolus is found near one of the poles of the spindle, and only takes 
up the cytoplasmic stain. This position was found to be characteristic of 
the stage. Humphrey ( 17 ) in an early paper figured large bodies of similar 
appearance during the metaphase of the reduction division of Osmunda and 
Allium , and it is possible that in these cases also the appearance may be 
explained by the persistence of the nucleolus. At this stage the chromo- 
somes are of rather irregular shape, and it is difficult to correctly ascertain 
the number present ; some are hook-like, others U-shaped, and yet others 
bent in two directions and elongated. The impression that more than six 
are present is given, and this may perhaps be explained by the division of 
one or more of the bivalent chromosomes into the constituent parts. 
A little later the last trace of the nuceolus is lost, and the spindle 
becomes more marked. The chromosomes take on their characteristic 
shapes and become arranged on the equatorial plate (Fig. 27). The number 
can now be easily counted, and six were found to be constantly present. 
The commonest form is the ring, but X- and U- figures are frequently met 
with. Transverse division now takes place in each chromosome, and this 
can be particularly well seen in the ring forms. These are attached to the 
spindle by a fibre on each of the opposite sides, and the first sign of 
division is the appearance of a break in each in the plane of the equatorial 
plate. This may take place on one side of the ring while the other is still 
intact (Fig. 28). Finally, two semi-circular portions are set free, but these 
almost at once become V-shaped, the spindle fibres being attached at the 
apex on the V (Fig. 29). The impression given that the fibres exert 
a pulling strain is very strong. As the chromosomes separate the V form 
becomes elongated, and soon changes to a Y-shaped figure with the long 
arm of the Y directed towards the pole (Fig. 29 ; the pair of chromosomes 
towards the centre of the spindle). The short arms of the Y remain thick, 
and an aggregation of chromatin is found at the distal end of the long arm, 
\vhile the central portion of the latter becomes thin and drawn out. The 
U-shaped forms divide so that the parallel arms are separated, and the latter 
at first remain short and thick. As the anaphase continues the chromosomes 
become thinner and more elongated, but on reaching the poles they again 
contract and thicken (Fig. 30). A polar view at this stage shows the six 
