Further Observations on the Nuclear Division 



of Noctiluca. 



By 



C. Ishikawa, Ph. D. 



Prof, of Zoology, College of Agrioilture, Imp. Univ., Tokyo. 



{With Plate XIX.) 



A. Centrosome, Centrosphere and Pole-Plate. 



In my former papers on Noctiluca ('94, h, c), I have shown 

 that a certain part of the cytoplasm situated close to the nu- 

 cleus which is preparing to divide, becomes transformed into a 

 large, spherical body, agreeing in all particulars with the archo- 

 plasm of higher animals. At the centre of this mass of cyto- 

 plasm, I have found, moreover, either a single body or a group 

 of smaller bodies, generally surrounded in either case by a clear 

 space, — structures which evidently correspond to the centrosome 

 or a group of centrosomes (Heidenhain '94, d). By division of 

 the centrosome and of the archoplasm surrounding it, a large 

 spindle is formed, which pushes itself against the nuclear wall 

 at one side so that the nucleus is turned into a half- ring form. 

 The division of tlie nucleus takes place much in the same way 

 as in higher forms, the only difierence consisting in the per- 

 sistence of the nuclear wall and the consequent modification in 

 the relative position of the spindle fibres and the chromosomes. 



