﻿100 Froceedinys of the Royal Physical Society. 



As division proceeds, the fibres which arise in the region 

 occupied by the karyosome become very distinct, and seem 

 (Figs. 43a-45) to stretch through the whole of either part of 

 the dividing nucleus, the halves of which become, as it were, 

 pushed apart. The nuclear membrane becomes less distinct, 

 and appears to divide across at the equator, and the chromo- 

 somes usually become quite confused. In about the middle 

 stage of division, it is to be noted that the fibres of the 

 mitotic figures are spread out at either (Fig. 46) nucleus over 

 quite a wide space — usually the whole width of the nucleus 

 — but are narrowed down towards the centre. The narrow- 

 ing of the fibres creeps, as it were, from the equator or centre 

 of the mitotic figure towards either nucleus, and it is now 

 found that they form an extraordinarily well-defined bar 

 (Fig. 47), whose attachment at the nuclear ends is, 

 curiously enough, connected with the reintegrating 

 " membrane." This point is exceedingly clear in some 

 cases. 



During the process of division there often, though not 

 invariably, appears to be a rotation of the axis of the whole 

 division figure through an angle of 90°. A glance at Figs. 

 45 and 46 makes this very obvious. ' 



The trophonuclei gradually become completely recon- 

 structed, and individuals are to be found showing two 

 perfectly definite nuclei with eight chromosomes and the ring 

 karyosome and a well-defined membrane, the two bound 

 together by a very straight and extraordinarily clear band 

 of fibres. The fibres may sometimes be so persistent as to 

 stretch between the nuclei after the protoplasm between 

 them has divided, cf. Fig. 48. There is an interesting re- 

 semblance between this bar and the flagellum, both as 

 regards its development and its optical appearance. 



Ultimately the band of fibres disappears, but it is to be 

 noted that it is not included in the nuclei, but vanishes in 

 the protoplasm. 



This form of division is a simple mitosis. An achromatic .i 

 nuclear figure is very definitely formed, and may, I think, ji 

 in some measure be compared to the axial fibres of more i 

 advanced types. There is no equatorial plate formed, nor ' 



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