268 J. E. S. MOORE. 



fine chromatic network of the resting nucleus first into the 

 lop-sided figure described by Hermann, and probably has a 

 good deal to do with the origin of the ten chromosomes on the 

 nuclear periphery (figs. 4 — 8). But the initial impulse which 

 starts such a fusion is an entirely different matter. This 

 might rise from a variety of causes, from a gradual increase of 

 internal pressure caused by osmotic action, or it might be pro- 

 duced by some change in that polarity supposed to exist 

 between the centrosomes lying close to its exterior; and it is 

 curious to note in this connection that the fusion in Branchipus 

 does start from that side where the most marked pseudosomes 

 exist (figs. 3, 4, 6, a, a) , and, if we may put the same interpretation 

 on the metamorphosis of other cells, Hermann's, vom Rath's, 

 and possibly Flemming's figures would be in complete accord- 

 ance with such a view. I very much doubt, however, if either 

 of these suppositions will be found to be the explanation of the 

 origin of the fusion in the first instance. But, if once started, 

 we have seen that the nuclear metamorphosis during karyo- 

 kinesis, from the resting stage up to that at which a limited 

 number of chromosomes exist on the periphery, is, to a certain 

 extent, the logical consequence of its progress. 



I have arranged the succeeding description in the light of 

 this conception because, since it has helped us thus far, we 

 might pre-suppose it useful in the elucidation of other karyo- 

 kinetic phenomena; and, unless I have done very indifferent 

 justice to the appearances before me, this supposition should be 

 fully justified. 



The ten ellipso-spherical chromosomes (figs. 5, 7) which 

 have arisen from an irregular transverse splitting, or, rather, 

 running into drops of the thickened chromatic network, after 

 it was brought by the progressive fusion to the nuclear 

 periphery, become rapidly constricted in the middle to form 

 the dumb-bell figures characteristic of these and many other 

 Arthropod nuclei (figs. 7 — 12). 



Each cell now contains ten double or twenty single chromo- 

 somes, i. e. double the ordinary number (figs. 7, 10, 12) ; and it 

 is interesting to compare such nuclear figures and their origin 



