502 



C. ISHIKAWA. 



Nuclear Division. 



In a short j)a]>er ^ sent to the Nahirforscli enden Gesellschaft zit 

 Freiburg im Breisgau, I treated at some length of the structure of the nu- 

 cleus in the resting stage, as well as of the peculiar manner in which 

 the division of the Noctiluca-nucleus takes place. As the present 

 account covers the same ground, some of the facts described in that 

 paper are necessarily repeated in this one. Nevertheless I do not 

 hesitate to go again over the same subject here, for two reasons, 

 namely : (a) many new facts have become known, and the nature of 

 some of the d(3ul)tfnl phenomena been ascertained since then ; (h) the 

 papers appeal to t^^•o ditferent sets of readers. 



1. Xuclens in resting stage: — The living nucleus appears quite 

 transparent and homogeneous, as all other observers of Noctiluca 

 have long ago described. It is covered by a rather thick membrane, 

 whose contour is often seen as double. When treated with reagents, 

 such as acetic acid, osmic acid, chromic acid, etc., a number of chroma- 

 tic bodies can e;isily be distinguished in it. These elements appear as 

 strino-s of deeply staining bodies which often take an S -form. Each 

 strino- consists, in well prepared specimens, of a luunber of disc-shaped 

 microsomes arranged one after the other like the chains of mammalian 

 red blood-corpuscles. Tliese strings lie either singly or, more often, 

 two or four united together. In the paper named above, I sup- 

 posed the single string to be primary, and the compounds of two 

 or four to be secondary, probably produced by division of the single 

 string. In accordance with this supposition, I designated the 

 number of chromosomes as ten. In many cases this number seems 

 to hold true, as Figs. o3, o4, 40-47 show ; but in other cases, such 



1 This pajjer was written for the l'\'xii<ch7-iffen couiuieuioratiug Prof. Weisuiann's 60th l.irth- 

 day which occurs on the I7th January, 1894. 



