THE STRUCTURE OF CELLS 



whilst the other is much poorer in chromatin. During mitosis the 

 two act as complements, the latter nucleus furnishing the spindle 

 apparatus, whilst the former supplies the chromatin. Much specu- 

 lation has been built on this case, which is assumed by some writers 

 to indicate that the centrosome or centrosphere is equivalent, 

 phylogenetically, to a nucleus. But it may be open to doubt 

 whether the facts in Paramoeba have really been correctly inter- 



Fio. 20. 



Acanthocystis andeata. A and B, forma- 

 tion of the centrosome from nuclear 

 constituents in swarm-spores. C, resting 

 cell. D, nuclear division preceding fission. 

 (After Schaudinn.) 



preted, in the sense of regarding the spindle-forming structure as a 

 genuine nucleus. 



Many cases are known in which bodies which represent centro- 

 somes originate from the nucleus, as appears certainly to be the 

 case in Actinosphaerium, and especially in Acanthocystis, as described 

 by Schaudinn. In the latter animal the ordinary nuclear divisions 

 are associated with the fission of a corpuscle or centrosome occupy- 

 ing a central position in the cell, the nucleus lying close to its side. 



