CHAPTER VIII 



SOMATIC MITOSIS AND CHROMOSOME INDIVIDUALITY 



SOMATIC MITOSIS 



Since the time when the cell was pointed out as the unit of structure 

 and function it has been recognized that the mode of origin of new cells 

 is a matter of fundamental importance. We have seen in our historical 

 sketch that cells were believed by the founders of the Cell Theory to 

 arise de now from a mother liquor, or "cytoblastema," a misconception 

 removed by later investigations in which it was shown beyond question 

 that cells arise only by the division of preexisting cells. By several early 

 observers the nucleus was seen to have a more or less prominent part in 

 the process, its division preceding that of the cell, but "it was not until 

 1873 that the way was opened for a better understanding of the matter. 

 In this year the discoveries of Anton Schneider, quickly followed by 

 others in the same direction by Biitschli, Fol, Strasburger, Van Beneden, 

 Flemming, and Hertwig, showed cell-division to be a far more elaborate 

 process than had been supposed, and to involve a complicated trans- 

 formation of the nucleus to which Schleicher (1878) afterward gave the 

 name karyokinesis. It soon appeared, however, that this mode of divi- 

 sion was not of universal occurrence; and that cell-division is of two widely 

 different types, which Van Beneden (1876) distinguished as fragmenta- 

 tion, corresponding nearly to the simple process described by Remak, 

 and division, involving the more complicated process of karyokinesis. 

 Three years later Flemming (1879) proposed to substitute for these 

 terms direct and indirect division, which are still used. Still later (1882) 

 the same author suggested the terms mitosis (indirect or karyokinetic 

 division) and amitosis (direct or akinetic division), which have rapidly 

 made their way into general use, though the earlier terms are often 

 employed. Modern research has demonstrated the fact that amitosis 

 or direct division, regarded by Remak and his followers as of universal 

 occurrence, is in reality a rare and exceptional process;. . . it is certain 

 that in all the higher and in many of the lower forms of life, indirect 

 division or mitosis is the typical mode of cell-division" (Wilson 1900, 

 pp. 64-65). 1 



1 The following additional historical data arc of interest. The chromosomes, 

 though they appeared in the figures of Schneider (1873), were first adequately drawn 

 by Strasburger in 1875. Longitudinal splitting was described by Flemming in 1882. 

 The terms prophase, mctaphase, and anaphase were introduced by Strasburger in 



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