354 BULLETIN OF THE 



the poles of the cask-shaped figure ; this fusion results in the production 

 of a homogeneous structure, which may have a somewhat irregular out- 

 line, — traces of its origin from distinct rods, — but which is only a tran- 

 sitional stage in the formation of the new nucleus. This homogeneous 

 structure breaks up into elements which exhibit the same irregular kary- 

 okinetic phenomena as the nucleus approaching division. . Ultimately a 

 part of the stout fibres arrange themselves to form a nuclear membrane, 

 which, however, does not enclose all the remaining nuclear elements, so 

 that a part of the karyokinetic mass in each half is not employed in 

 forming the new nuclei. 



A summary of Schleicher's theoretical considerations is not easily 

 brought within narrow limits. The reader must therefore be referred to 

 the original for a complete exposition of the views entertained by the 

 author. 



In the metamorphosis of the old nucleus into a karyokinetic mass, the 

 chemical outweigh the purely physical activities ; new chemical products 

 make their appearance ; it is not a simple mechanical separation of the 

 less from the more fluid constituents. 



The membrane and the "nuclear stuff" (i. e. the inner nuclear sub- 

 stance) differ chemically, for the latter must suffer a chemical change 

 before the two can unite. The growth of the nucleus during the karyo- 

 kinetic period, by which a division is made possible, is at the expense 

 of the enumerated protoplasmic structures ; the latter, in turn, arise by 

 a process of chemical differentiation, which is most active in the periph- 

 ery of the cell. The growth of the nucleus is not brought about by a 

 process of intussusception, but by the juxtaposition of visible granules. 

 During the protracted karyokinetic period, unknown physical forces 

 arise, which become recognizable at the moment of division in the sud- 

 den separation of the halves of the structure by repulsion. The as- 

 sumption that the division takes place in obedience to two centres of 

 attraction formed at the middle of each of the prospective daughter cells, 

 is negatived by the fact that the position of such centres of attraction 

 are conditioned by, and dependent upon, the distribution of the proto- 

 plasm, — the shape of the cell, in other words. It follows that in an 

 elongate cell these centres would lie toward the poles, and the division 

 would therefore have to take place in the direction of [perpendicular 

 tol] the longest diameter; this, however, the author's observations 

 show, is not always the case. 



The so-called nuclear sap is an important material, without the pres- 

 ence of which the homogeneous karyokinetic halves could not attain the 



