GROWTH AND SENESCENCE 



57 



and (3) there are relatively abrupt breaks between these cycles, 

 the degree of abruptness being of the order of metamorphosis 

 in cold-blooded animals. 



The broken curves in Figure 36 were drawn in on the as- 

 sumption that such phases of constant percentage rates of 

 growth are present and that they are separated by breaks. In 



Pep cent 

 pepdey 



2 40 



P 



P-830 

 1 



k.= -^=mK-inw, 



Rat,?,unmated 



Figure 39. The value of k (relative rates of growth) plotted 

 against age. 



other words, the up-and-down fluctuations do not represent 

 cycles of the kind shown in Figure 35, but rather successive 

 segments of constant growth rate, separated from each other by 

 relatively abrupt changes, which may be termed "metamor- 

 phoses." 



If the percentage rates of growth (i.e., 100^ in Figures 36 

 and 39) are plotted against age, we obtain Figure 39, which 

 exhibits the conception of "metamorphosis" in warm-blooded 

 animals in quite a spectacular fashion. 



According to Figures 37 and 39, the percentage rate of 

 growth in the rat for the earliest period for which data are 



