SPINDLE-POLES 533 



that a sudden change of charge at the poles determined a sudden 

 change from repulsion at metaphase to attraction at anaphase 

 (Kuwada, 1928). Such an assiunption is difficult a priori when 

 appUed to an ideal meiosis, but is altogether impossible when 

 applied to cases of non-congression, non-pairing and non-orienta- 

 tion at meiosis, and its application to mitosis has never even been 

 attempted. 



The fact that the later anaphase movement is not due to the action 

 of forces at a distance, but to the spindle stretching, has some bear- 

 ing on this old theory that the chromosomes move primarily by 

 attraction to the poles and not by repulsion from one another. If 

 this theory were valid the forces should, on all analogy, increase in 

 effect as the chromosomes approach the poles ; evidently they 

 diminish, as they should if they are repulsions between the chromo- 

 somes which are moving apart. 



With the present hypothesis the continuous action of the centres 

 of repulsion on one another and on the spindle, having a ciunulative 

 effect in increasing the efficiency of those repulsions, is capable of 

 explaining the series of movements that make up metaphase and 

 anaphase in terms of changing equilibria. In order to see exactly 

 how these equilibria will change we must examine in more detail 

 the organs of movement, the centrosomes and centromeres. 



(v) The Organs of Movement. {a) The Centrosomes. The 

 centrosome is a body associated in its cycle of division and in its 

 apparent function with the nucleus. During the resting stage it lies 

 inside the micro-nuclei of ciliates, but elsewhere as a rule just out- 

 side the nucleus. In Aggregata it probably enters the nucleus at 

 telophase (Belar, 1926). It can be found in every stage of the Hfe- 

 history in many -protozoa and higher animals ; but even in these it 

 fluctuates in different tissues and different stages of its cycle both in 

 its staining capacity and in its apparent influence on the cytoplasm 

 around it {e.g., Piscicola, Geitler, 1934). In the resting stage it is 

 most difficult to see, and its continuity, like that of the chromo- 

 somes themselves, is best shown in rapid divisions such as the cleav- 

 age mitoses in Echinoderms. In many organisms it is visible only 

 at certain stages of development ; in mosses, ferns and Cycads, for 

 example, it is found only in the cells forming spermatozoids (cf. 



