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no longer even approximately straight. Each is Y-shaped, with the 
angle turned towards the pole which it approaches (fig. 43). Thus in 
the interval between the formation of the nuclear plate and the com- 
plete separation of each chromosome into two segments, the shape of 
Fig, 42. Fig. 4:>. Fig. 44. 
each segment has changed from the half of an approximately straight 
rod to an acute-angled Y. A complete study of the stages inter- 
mediate between these extremes is necessary to determine how this 
change occurs. The view hitherto accepted is that as the free end, 
or limb (T) of the segment lengthens at the expense of the other end 
or trunk (t), it bends outwards with reference to the whole spindle 
(fig. 44).* Such intermediate forms as those figured in fig. 44 
support this theory. 
The view advanced by Professor Farmer and Mr. Belajeff inde- 
pendently of each other differs widely from this. They have come 
to the conclusion that a second longitudinal fission exists in the 
chromosome besides that along which the actual separation takes 
place. The relative positions of these two fissions are shown in fig. 
45. A is a diagram of a chromosome seen in profile, B a diagram of 
Fig. 45. Fig. 46. 
A B 
it 
the same chromosome seen end-on. The fission shown in A along the 
line a, a, is that along which the separation of the segments actually 
takes place. The second fission along b , b, is visible in B. It is 
* Strasburger , 1 Controversen der indirecten Kerntheilung/ p. 31. L. Guignard, 
op. cit., p. 176. 
