IV] STRUCTURE OF THE CELL 195 



of the chemical, electrical or other forces which are associated 

 with it. But there is another consideration which would lead us 

 to suspect that many features in the structure and configuration 

 of the cell are of very secondary biological importance ; and that 

 is, the great variation to which these phenomena are subject in 

 similar or closely related organisms, and the apparent impossibility 

 of correlating them with the peculiarities of the organism as a 

 whole. "Comparative study has shewn that almost every detail 

 of the processes (of mitosis) described above is subject to variation 

 in different forms of cells*." A multitude of cells divide to the 

 accompaniment of caryokinetic phenomena ; but others do so 

 without any visible caryokinesis at all. Sometimes the polarised 

 field of force is within, sometimes it is adjacent to, and at other 

 times it Hes remote from the nucleus. The distribution of potential 

 is very often symmetrical and bipolar, as in the case described; 

 but a less symmetrical distribution often occurs, with the result that 

 we have, for a time at least, numerous centres of force, instead 

 of the two main correlated poles : this is the simple explanation 

 of the numerous stellate figures, or " Strahlungen," which have 

 been described in certain eggs, such as those of Cliaetofterus. In 

 one and the same species of worm {Ascaris megalocefhala), one 

 group or two groups of chromosomes may be present. And 

 remarkably constant, in general, as the number of chromosomes in 

 any one species undoubtedly is, yet we must not forget that, in 

 plants and animals alike, the whole range of observed numbers is 

 but a small one; for (as regards the germ-nuclei) few organisms 

 have less than six chromosomes, and fewer still have more than 

 sixteen t- In closely related animals, such as various species of 

 Copepods, and even in the same species of worm or insect, the 

 form of the chromosomes, and their arrangement in relation to 

 the nuclear spindle, have been found to differ in the various ways 

 alluded to above. In short, there seem to be strong grounds for 

 beheving that these and many similar phenomena are in no way 

 specifically related to the particular organism in which they have 



* Wilson. The Cell. p. 77. 



t Eight and twelve are by much the commonest numbers, six and sixteen 

 coming next in order. If we may judge by the list given by E. B. Wilson {The 

 Cell, p. 206), over 80 % of the observed cases lie between 6 and 16, and nearly 

 60 % between 8 and 12. 



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