CONSTANT DIFFERENTIAL GROWTH-RATIOS 33 



the large chela has 

 attained half the 

 rest-of-body size 

 when the total weight 

 is about 1-65 g. If 

 the animal could grow 

 to 24 g. (less than 

 30 per cent, bigger 

 than the biggest U. 

 minax) , its large chela 

 would be the same 

 weight as all the 

 rest of it together. 

 Twenty-four grams 

 is a very small weight 

 for many crabs, in- 

 cluding forms of sim- 

 ilar semi-terrestrial 

 and burrowing habits 

 to Uca, such as Ocy- 

 poda, yet no species 

 of fiddler-crab has 

 grown to a size much 

 over that of U. 

 minax. It may thus 

 be plausibly sug- 

 gested that the exist- 

 ence of this continu- 

 ously high growth- 

 ratio in the large 

 claws of the male 

 fiddler-crabs may 

 have acted as a 

 limiting factor in 

 their size-evolution, 

 any possible advan- 

 tage to be obtained 

 by increase in size 

 not countervailing to 

 cause selection to 

 alter the chela's 

 growth-mechanism . 

 Analysis of the 

 3 



3 4 5 6 7 8 



carapace length, cm. 

 A 



zzo 



2-00 



/■BO 



1-60 



/■40 



I 20 



100 



log carapace length, mm. 



120 



B 



1-60 



Fig. 21. — Relative growth of male and female 



chelae. (A) in Palaemon carcinus, (B) Palaemon 



bengalensis ; logarithmic plotting. 



(From data of Kemp, I9i3- X 5-) 



