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MUUIKL KOI5KKTS0N AND E. A. MINCHIN, 



SuMMAItY AND CONCLUSIONS. 



The course of events that take place in the division of 

 the collar-cells may be summarised briefly as follows, omitting 

 the details of the mitosis, since they present no special 

 peculiarities. 



The nucleus of the collar-cell migrates from the base to 

 the apex of the cell, and so comes to lie immediately under 

 the blepharoplast. The flMgellum then disappears and the 

 blepharoplast divides. The two daugliter-blepharoplasts 

 travel to opposite sides of the nucleus and take on the function 

 of centrosomes. The nucleus breaks up into chromosomes, 

 its membrane disappears, and a mitotic spindle is formed in 

 the ordinary way, with the two centrosomes at its poles. 

 The two new flagella then at once begin to grow out from 

 the two centrosomes, outside the original collar, before the 

 equatorial plate is divided. The mitosis is completed, and 

 as the cell-body divides the original collar breaks down and 

 disappears. The centrosomes become the blepharoplasts of 

 the two daughter-cells, the flagella continue to grow out from 

 them, the new collars grow up round the new flagella, the 

 reconstituted daughter-nuclei migrate back again to the 

 bases of the cells, and the two daughter-cells resume the 

 structure and appearance of the ordinary resting collar-cells. 

 Thus it is seen that the blepharoplast-centrosome is a 

 permanent cell-organ, which multiplies with the cell ; but 

 that the collar and flao-ellum are formed afresh at each cell- 

 division, quite independently of the collar and flagellum of 

 the parent cell. 



In this process of division the feature to which we wish 

 to draw special attention is the fact that the bodies which 

 have the function of blepharoplasts in the resting-cell have 

 that of centrosomes in the dividing cell. In fact, it is seen 

 that during a certain stage in the division, the stage, namely, 

 of the nuclear spindle, when the daughter-flagella are growing 

 out from the centrosomes at the poles of the spindle, one and 



