^73 )([M,j^ J 



III] OF UNEQUAL GROWTH 207 



interest law, which (calhng y and x the weights of the claw and of 

 the rest of the body) may be expressed by the usual formula for 

 compound interest, 



y = bx^, or log y = \ogb + k log x; 



and the coefficients (6 and Jc) work out in the case of the fiddler-crab, 

 to begin with, at 



2/ = 0-0073 xi-«2. . 



300 



100 200 300 400 500 600 700 

 Weight of body (mgm.) 



Eig. 54. Relative weights of body and claw in the fiddler- 

 crab { Uca 'pugnax). 



But after a certain age, or certain size, th^e coefficients no longer 

 hold, and new coefficients have to be found. Whether or no, the 

 formula is mathematical rather than biological; there is a lack of 

 either biological or physical significance in a growth-rate which 

 happens to stand, during part of an animaFs fife, at 62 per cent, 

 compound interest. 



Julian Huxley holds, and many hoki with him, that the exponential 

 or logarithmic formula, or the compound-interest .law, is of general 

 application to cases of differential growth-rates. I do not find it to 

 be so : any more than we have found organ, organism or population 

 to increase by compound interest or geometrical progression, save 



