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the fission. It would therefore he difficult to conceive an incurving 
limb straightening, or a straight limb curving inwards, but it is easy 
to imagine a straight limb curving outwards. 
The chromosomes with incurved limbs commonly have their free 
ends pressed together at this stage (fig. 48 a), but examples with the 
ends barely touching, or quite free, are numerous. 
3. The difficulty of interpreting the forms of chromosomes in these 
later stages arises from the fact that as the limb l in such a figure as 
fig. 49 increases in length at the expense of the trunk t they soon become 
of about equal length and are hardly to be distinguished from each 
other (fig. 50). This is emphasised by the tendency of the figure to 
become pinched up as if it were hinged at e e , so that limb and trunk 
lie close together and almost parallel (fig. 50). The front view of a 
Fig. 49. Fig. 50. Fig. 51. 
chromosome in this stage resembles fig. 51. When, as often happens,, 
the elbows e e curve outwards or inwards (see arrows in fig. 50) the 
appearance of the chromosome in front is that of fig. 46a, in three- 
quarters view that of 4 66. 
The uniformity of shape of the chromosomes in the spindle just 
before the diaster stage begins, is very remarkable. The great 
majority of chromosomes are of the shapes figured in figs. 46 and 51, 
and the whole figure certainly recalls the “ tonnen-form ” in Flemming’s 
drawings of heterotype division. I have suggested in figs. 47 a, 48 a, 49, 
and 50 how a chromosome Ivith incurved limb may assume the appear- 
ance of fig. 51 (front view). A similar series is easily constructed 
for chromosomes with outcurving limbs (cf. fig. 44). Most straight 
limbed chromosomes curve outwards in later stages, but a few con- 
tinue straight after separation and never assume the Y-shape at all. 
The discussion of other irregularities must be postponed. 
It will be seen that the explanation just given of the assumption 
of the Y-shape by the segments of chromosomes as they separate 
differs only in detail from that hitherto accepted. I believe that the 
appearances shown in fig. 46 are the result of the bending of the 
segments and are independent of any partial fission. There is no 
doubt, however, that the process is more complicated than was 
formerly thought. 
