THE EVOLUTION OF THE CELL. Ill 



BY THE LATE PROFESSOR E. A. MINCHIN, F.li.S. 



In the phase of evolution that I have termed the pseu- 

 domoneral or cytodal phase, in which the organism was 

 a droplet of periplasm containing scattered biococci or 

 chromidiosomes, metabolism would result in an increase 

 in the size of the cytode-body as a whole, accompanied by 

 multiplication of the chromidiosomes. Individualization 

 of the eytodes would tend to the acquisition of a specific 

 size, that is to say, to a limitation of the growth, with the 

 result that when certain maximum dimensions were at- 

 tained the whole cytode would divide into two or more 

 smaller masses amongst which the chromidiosomes would 

 be partitioned. 



In the next stage of evolution, the protocyte with a defi- 

 nite nucleus, it is highly probable that at each division of 

 the cell-body, whether into two or more parts, the primi- 

 tive method of division of the nucleus was that which I 

 have termed elsewhere ' ' chroniidial fragmentation"; 28 

 that is to say, the nucleus broke up and became resolved 

 into a clump of chromidiosomes, which separated into 

 daughter-clumps from which the daughter-nuclei were 

 reconstituted. Instances of nuclear divisions by chro- 

 midial fragmentation are of common occurrence among 

 the Protozoa and represent probably the most primitive 

 and direct mode of nuclear division. 



It is clear, however, that if the chromatin-grains are to 

 be credited with specific individuality and qualitative dif- 

 ferences amongst themselves, this method of nuclear divi- 

 sion presents grave imperfections and disadvantage-, 

 since even the quantitative partition of the chromatin is 

 inexact, while the qualitative partition is entirely fortu- 

 itous. Chromidiosomes having certain specific proper- 

 ties might all become accumulated in one daughter-cell, 



26 Op. cit., p. 101. 



271 



