DYNAMICS OF MORPHOGENESIS 193 



All results obtained thus far from experiments by the direct 

 method on animals of different ages, whatever the species, are 

 essentially similar to those of table 9. On page 165 the records 

 of a series with asexually produced young and old indi\aduals of 

 Plan aria dorotocephala are gi^Tn to illustrate the method of 

 recording data. There also the young animals begin to disin- 

 tegrate earlier and disintegrate more rapidly than the older. 



"VMien we compare these results with the other lines of evidence 

 it is clear that all are in essential agreement. The only possible 

 factor that can be responsible for the observed differences in 

 physiological resistance is the rate of reaction in the organism. 



In the paper on senescence two series are presented showing 

 the differences between young and old animals from nature by the 

 indirect method (Child '11 a, pp. 544-547, figures 1 and 2; figure 

 2 is reproduced as figure 1 of the present paper). Other figures 

 show similar differences produced in a variety of ways: for exam- 

 ple, figures 3 to 7 of that paper show differences in resistance, i.e., 

 in rate of reaction produced by differences in nutrition and figures 

 9 to 14 show how pieces may become physiologically young as 

 the result of regulation. 



By the indirect method the animals with the higher rate of 

 reaction show the higher resistance, viz., they become more readily 

 and more completely acclimated. 



5. Further miscellaneous evidence 



Further e\'idence for tlje existence of a relation between physio- 

 logical resistance and rate of reaction is obtained from various 

 other lines of experimentation which will be considered fully in 

 other connections. 



By means of the direct method it is possible to distinguish the 

 change in rate due to various forms of stimulation. For example, 

 a piece isolated by cutting has, during the first few hours after 

 the section, a much lower resistance, i.e., a much higher rate 

 of reaction, than the same region of the uninjured body. This 

 method shows further that the resistance of such pieces gradually 



