CONSTANT DIFFERENTIAL GROWTH-RATIOS 31 



differentiation. It may (like Boyle's law) prove only to be 

 an approximation, and to be capable of modification in cer- 

 tain circumstances ; yet (again like Boyle's law) it may remain 

 fundamental. 



We may now proceed to consider a little more in detail 

 some of the cases. In the first place, we can utilize our formula 

 to deduce the moment of onset, in male Uca pugnax, of the 

 large chela's heterogony. To do this we must first know the 

 weight of the small claw. This in males is identical in form 



mqr. 

 100 



50 



I 



• 10 



k 5 



1 2 5 10 20 50 100 200 mgr. 



body - weight 



Fig. 20. — Increase of water-content with total weight in the larva of the 



wax-moth, Galleria ; logarithmic plotting. 

 k for fresh weight, early phase i-o, late phase i-o ; for dry weight, early phase 0-96, late phase 0-91. 



with both claws of females, and does not change its relative 

 weight with increasing body-size : at all stages it weighs, as 

 does a single female chela, almost precisely 0-02 of the rest- 

 of-body weight. If we make the assumption that our formula 

 for the first phase holds from the first moment of increase of 

 the large chela, we have simply to extrapolate from our formula 

 and find the point on the curve at which rest-of-body weight 

 is fifty times chela weight. This is found to be close to 5 mg. 

 body- weight, when the chela should weigh o-i mg. 



