HEREDITY AND EVOLUTION 103 



We can but glance at one or two of the most 

 significant features of karyokinetic division. The 

 most striking and telling of these is the contrast 

 so often shown between the distribution of the 

 nuclear and of the protoplasmic elements. With 

 certain exceptions in the phenomena of matura- 

 tion, which only bring fresh support to the general 

 principle, nuclear division is both quantitatively 

 and qualitatively exactly equal. Protoplasmic 

 division is often both quantitatively and quaUta- 

 tively unequal, separating substances that have 

 been proved by precise experiment to be of dif- 

 ferent physiological value. But more than this, 

 the formation and division of chromosomes effect 

 not merely a mass-division of the chromatin but 

 an equal meristic division of its whole substance; 

 and as Wilhelm Roux first urged, we can find no 

 meaning in the whole elaborate process if the 

 chromatin be not composed of qualitatively dif- 

 ferent elements that require equality of distribu- 

 tion. That such is really the constitution of the 

 chromatin can no longer be doubted by any who 

 are familiar with the evidence. If the chromo- 

 somes be not actually persistent individuals, as 

 Rabl and Boveri have maintained, they must at 

 least be regarded as genetic homologues that are 

 connected by some definite bond of individual 

 continuity from generation to generation of; 

 cells. And the evidence has steadily accumulated! 

 to show that the chromosomes exhibit definite 

 qualitative differences. In many animals and 



