IV] OF CHROMOSOMES 339 



the germ-nuclei) few have less than six chromosomes, and few have 

 more than twenty*. 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 ways alluded to 

 above ; while only here and there, as among the chrysanthemums, 

 do related species or varieties shew their own characteristic chromo- 

 some numbers. In contrast to the narrow range of the chromo- 

 some numbers, we may reflect on the all but infinite possibilities of 

 chemical variabihty. Miescher shewed that a molecule containing 

 40 C-atoms would admit (arithmetically though not necessarily 

 chemically) of a million possible isomers; and changes in position 

 of the N-atoms of a protein, for instance, might vastly increase 

 that prodigious number. In short, we cannot help perceiving 

 that many nuclear phenomena are not specifically related to the 

 particular organism in which they have been observed, and that 

 some are not even specially and indisputably connected with the 

 organism as such. They include such manifestations of the physical 

 forces, in their various permutations and combinations, as may also 

 be witnessed, under appropriate conditions, in non-living things. 

 When we attempt to separate our purely morphological or "purely 



* The commonest numbers of (haploid) chromosomes, both in plants and 

 animals, are 8, 12 and 16. The median number is 12 in both, and the lower 

 quartile is 8, likewise in both; but the upper quartile is 24 or thereby in animals, 

 and in the neighbourhood of 16 in plants. If we may judge by the long lists given 

 by E. B. Wilson (The Cell, 3rd ed. pp. 855-865), by M. Ishikawa in Botan. Mag. 

 Tokyo, XXX, 1916, by M. J. D. White in his book on Chromosomes, or by Tischler 

 in Tabulae Biologicae (1927), fully 60 per cent, of the observed cases lie between 6 

 and 16. As Wilson says (p. 866) "the number of chromosomes is per se a matter 

 of secondary importance"; and (p. 868) "We must admit the present inadequacy 

 of attempts to reduce the chromosome numbers to any single or consistent 

 arithmetical rules." Clifford Dobell had said the same thing: "Nobody nowadays 

 will be prepared to argue that chromosome numbers, as such, have any quantitative 

 or qualitative relation to the characters exhibited by their owners. Complexity 

 of bodily structure is certainly not correlated in any way with multiplicity of 

 chromosomes " ; La Cellule, xxxv, p. 188, 1924. On the other hand, Tischler stoutly 

 maintains that chromosome-numbers give useful evidence of phylogenetic affinity 

 {Biol. Centralbl. XLvni, pp. 321-345, 1928); and there axe a few well-known cases, 

 such as the chrysanthemums, where, undoubtedly, the numbers are constant and 

 specific. Again in certain cases, the number of the chromosomes may- differ in 

 dififerent races (diploid and tetraploid) of the same plant; and the difference is 

 accompanied by differences in cell-size, in rate of growth, and even in the shape 

 of the fruit (of. Sinnott and Blakeslee, Xat. Acad, of Sci. 1938, p. 476). 



