BINUCLEATE CELLS IN TISSUE CULTURES. 101 



The process of nuclear amitosis is slow, excepting the final stage, which is rapid. 

 There seems to be a critical point in nuclear constriction ; before this point is reached 

 the nucleus may return to its original form, but after it has been passed the cleavage 

 of the nucleus jjroceeds rapidly, and results in two separate nuclear parts. 



Division of the nucleolus is not an essential of amitotic nuclear division; it may, 

 however, be concerned with the size of the nuclear fragments. 



There is no evidence of a form of nuclear amitosis that depends upon the for- 

 mation of an intranuclear membrane which subsequently Rjjlits. Such a structure 

 is simulated by the a})posed surfaces of the nuclear membranes of the parts of the 

 nucleus of a binucleate cell, when they are in close contact. Sometimes, also, 

 nucleoli, mitochondria, and inbending of the nuclear wall may resemble such a 

 membrane. 



Fate: There is no e\idence that direct division of the cytoplasm follows direct 

 division of the nucleus; thus amitosis is not a method of complete cell division, but 

 is to be looked upon as a change in form of a healthy nucleus. 



The regular process of mitosis may occur in binucleate cells. During this 

 jjrocess the chromatin material from both nuclear portions is merged into one 

 equatorial plate of chromosomes, the spiremes, which begin to arise separately in 

 the two nuclear parts, joining together to form the chromosomes. Furthermore, 

 this is the only kind of cell division which was found to occur in binucleate cells; 

 they either divide by mitosis or remain as they are, without fission of the protoplasm. 



The separate parts of the double nucleus have no reproductive independence 

 (though they may have metabolic independence), and act as a unit in mitosis. 

 Hence the reproductive capacity of the bipartite and monopartite nucleus is the same. 



Mitosis occurred as frequently in the binucleate as in the mononucleate cells. 



Nuclear fusion, without mitosis, has not been foimd to occur. 



GENERAL. 



Mitosis occurs in a nucleus irrespective of its shape; thus the spireme was 

 found in nuclei of rounded form, in those presenting equatorial constriction, and 

 in those divided into two portions. 



Chromosome hypothesis: Nuclear amitosis is not incompatible with theories of 

 inheritance which assume that the chromosome is the bearer of hereditary characters. 



(riant cells: The binucleate cell seems to be the first stag(^ in the formation of 

 the giant cell, which probably arises by a repetition of luiclear amitosis. This 

 conception does not include the formation of the foreign-body giant cell. 



Nuclear fragmentation was found to occur where conditions for life were not 

 favorable, and was thus a form of degenerative change. Fission of a healthy nucleus 

 (amitosis) must thus be distinguished from fission of an unhealthy nucleus (frag- 

 mentation) . 



Karyosomes of the cells examined were irregulai- in shape, underwent continu- 

 ous change in morphology, size, numbei-, and position, and were made up of numer- 

 ous closely j)acked masses of gel, encli with a core of greater density. 



The centrosphere in the cells examined was a slight!}' concentrated gel containing 

 a centrosome (usually paired). Its border is irregular, and this undergoes continu- 



