8o 



PROBLEMS OF RELATIVE GROWTH 



ilea pugnax 

 6 large claw 



i> 



the full implications of his ideas, which only became clear on 

 re-reading his book after obtaining certain empirical results 

 for myself. 



The starting-point of these investigations was afforded by 

 the fact, obvious to simple inspection, that whereas the pro- 

 portions of the separate joints of the female-type chelae in 

 the sexes of Uca do not change appreciably during growth, 

 those of the joints of the large or male-type chela do change, 



and very markedly. 

 The most obvious alter- 

 ation is a relative in- 

 crease of the size of the 

 propus with absolute 

 increase of the size of 

 the whole chela. How- 

 ever, when the weights 

 o f different chela- 

 regions were accurately 

 determined, it was 

 found that there existed 

 within the limb what 

 we may call a growth- 

 gradient, the distal re- 

 gion (chela + propus) 

 having the highest rela- 

 tive growth-rate, the 

 central region (carpus) 

 the next highest , and the 

 basal region, nearest the 

 breaking-joint, (merus 

 + part of ischium) the 

 lowest, although its 

 relative growth-rate 

 was still above that of 

 the body. 

 If we put this crudely into graphic form, using growth- 

 coefficients as ordinates and spacing the different regions 

 arbitrarily along the *-axis, we obtain a curve representing 

 the distribution, along the main axis of the limb, of what we 

 may for brevity's sake, without introducing any theoretical 

 ideas, speak of as growth-potential. This curve is inclined to 

 the horizontal, and is therefore the graphic representation of 

 a growth-gradient within the appendage, the inclination of the 



carpus 



Fig. 44. — Graph to show different relative 



growth-rates of different parts of the large 



claw of the fiddler-crab, Uca pugnax. 



Weights in mg. of dactylus + propus (o, scale on right) 

 and merus + ischius (+, scale on left) against weights of 

 carpus ; logarithmic plotting. The distal region shows 

 positive heterogony (k about 1-05) relative to the inter- 

 mediate region (carpus) ; the proximal region shows nega- 

 tive heterogony {k about 0-9). (See Table VI.) 



