ASPECTS OF KINETIC EVOLUTION 331 



suffice for one hundred generations of unicellular organisms 

 but might provide only one compound individual. Plants and 

 lower animals can be grown from cuttings or will regenerate 

 lost parts, but among the higher animals these powers of 

 asexual reproduction gradually disappear. 



Divergence from the normal may occur at any stage in the 

 development of the individual, which also varies continuously, 

 and not merely in the germ-cell. If the life-history of a very 

 simple animal or plant be considered, the concentration of in- 

 terest on one point tends to disappear. The processes of growth 

 and the preparation for spore-formation in such an organism as 

 Spirogyra do not appear less interesting or less fundamental 

 from the biological standpoint than conjugation and reproduc- 

 tion. Moreover, we now know that adaptations arise inside of 

 cells as well as outside. The chromosomes and centrosomes, 

 no less than the larval stages of insects, may prove to be re- 

 sultant phenomena of evolution, rather than causal or truly 

 primitive. 



It is easy to understand how those who have approached 

 evolution through the study of complex and specialized higher 

 groups should be led to think of heredity as a mechanism, but 

 if we take our standpoint at the other end of the organic crea- 

 tion it becomes apparent that heredity is merely a name for the 

 fact that cell divisions by which organisms are built up follow 

 closely similar lines in each successive generation. Organisms 

 are not different merely because they are built of different 

 kinds of cells, nor merely by reason of different arrangements 

 of the same kinds of cells. Both causes of difference are 

 present together in all the higher groups. Both kinds of dif- 

 ferentiation have gone forward simultaneously and it need not 

 be thought more wonderful that the cells of the same compound 

 individual are different than that different species should be 

 found among unicellular organisms. Indeed, heredity is most 

 perfect when the cells formed by successive divisions are all 

 alike. It maybe deemed a departure from strict heredity when 

 the)' become diversified, as in higher organisms. But whether 

 the individual consists of a single cell or of a colony formed 

 by many cell divisions, we are still dealing with the same 



