MORPHOLOGY 



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In the meantime other definite processes have been taking place ; 

 while the thread of the nuclear network has been shortening and dis- 

 entangling, the two centrospheres (1, c), previously lying together close 

 to the nuclear membrane, have separated and taken up a position 

 opposite each other (2, c). They constitute the poles of the division 

 figure. Beginning at these two points, the nuclear membrane dis- 

 appears, and the nucleoli also become more or less completely 

 dissolved, influenced in all probability by the centrospheres. Spindle 



Fig. 62.— Successive stages in nuclear and cell division, c, Centrospheres ; n, nucleolus ; s, chro- 

 mosomes ; sp, spindle fibres; A, B, C, chromosomes, showing longitudinal division and the 

 arrangement of the chromatin, (x circa 600.) 



FIBRES then arise from protoplasmic threads found within the nuclear 

 cavity, presumably with the co-operative activity of the nucleolar 

 substance. The spindle fibres converge towards both poles of the 

 division figure, and, viewed as a whole, they have the form of a spindle. 

 While some of the spindle fibres extend uninterruptedly from pole to 

 pole, others become connected with the chromosomes. Through this 

 arrangement of the spindle fibres, the position of the nuclear plate in 

 the equatorial plane of the spindle figure is determined ; while by the 

 contraction of the spindle fibres in connection with the chromosomes, 



