674 president's address. 



and a field in which the activities of the nucleus could be exer- 

 cised, not capable of initiating any important changes, and taking 

 only a passive part in cell-multiplication and reproduction. Cer- 

 tain changes which take place in the cell-})rotoplasm during these 

 processes were usually supposed to be brought about more or less 

 mechanically as a result of the changes that take place in the 

 nucleus itself. The appearance of the bodies termed "attraction 

 spheres" and " centrosomes" first discovered by E. van Beneden,* 

 with the nuclear spindle, was regarded as a phenomenon quite 

 subordinate in importance to the division of the chromatin sub- 

 stance of the nucleus itself. But since it has been shown that 

 the centrosomes and attraction-spheres become prominent before 

 the chromosomes actuallyfundergo division, and particularly since 

 it has been found that the attraction-spheres and central corpuscles 

 are capable of determination in cells which do not multiply 

 mitotically,'!' it has seemed probable to the majority of the investi- 

 gators of cell-structure that in these bodies we may have to 

 recognise independent centres of activity within the cell apart 

 from the nucleus. Moreover the behaviour of these bodies during 

 mitotic cell-division appears to indicate in no uncertain manner 

 that they have a part of importance to play in the process. The 

 fibrillse of the spindle appear to go out from the centrosomes to 

 become connected with the chromosomes, and it seems to be by a 

 movement of contraction of these fibrils that the two sets of 

 divided chromosomes are drawn apart towards the poles of the 

 spindle. Flemming in a recent addressj expresses himself in the 

 following terms with reference to the importance of these bodies : 

 — " Wir haben die Aussicht dass an die Kenntniss dieser 



* " Recherches siir la maturation cle I'ceuf, la f^condation et la division 

 cellulaire" (1883) ; and Van Beneden et Neyt, "Nouvelles recherches sur la 

 fecondation et la division mitosique." Mem. Acad. Roy. Belg. 1887. 



t First by Flemming (" Attraktionsphiiren und Centralkurpes in Gewebs- 

 zellen und Wandei'zellen," Anat. Anz. VI. 1891) ; afterwards confirmed by 

 Heidenhain (" Ueber die Centralkorperchen und Attraktionsphiiren der 

 Zellen," Anat. Anz. VI. (1891). 



J " Ueber Zelltheilung," Verhandl. d. Deutsch. Anat. Gesellsch. 1891. 



