GROWTH-GRADIENTS & GROWTH-INTENSITY 83 



arbitrarily represent the centres of homologous regions as 

 equidistant along the abscissa axis, and shall use the ^-values, 

 as obtained from the formula for constant differential growth- 

 ratios, as reasonable approximations for the values of growth- 

 intensity. 



§ 2. Steepness of Growth-gradient within an Organ 

 and Growth-intensity of the Organ as a whole 



The fact of a growth-gradient once established for the 

 heterogonic chela of Uca, the next step was to see if similar 

 growth-gradients occurred in other heterogonic organs. This 

 proved to be the case. We will first take other examples 

 from Crustacean appendages. The weights of the separate 

 joints of the chela (five of them distal to the breaking- joint) 

 were taken for both male and female Maia squinado (Huxley, 



-10 

 c // 



£ 10 





OS 





 §>*« 



•a-"" ^ 



merits + 

 ischium 



carpus 

 axis of chela. — 



dactylus 

 + propus 



Fig. 45. — Growth- gradient in the large chela (x) of the fiddler-crab, Uca, 



(©) of the spider-crab, Maia. 



The growth-coefficients of the different regions are here taken relative to the total weight of the 

 chela distal to the breaking-point, not, as in Fig. 44, to the carpus-weight. 



1927, and unpublished). It was found that while the pro- 

 portionate weight of the joints of the female chela remained 

 approximately constant within the limits of variation at all 

 absolute sizes, — i.e. their growth-coefficients relative to the 

 chela as a whole, like that of the chela relative to rest-of- 

 body, were all = i-o, — those of the male chela during its period 

 of heterogony were all greater than unity and were arranged 

 in a regular growth-gradient. This was double in form, with 

 high point in the propus, a slight fall towards the tip (dactylus), 

 and a more rapid and more prolonged fall towards the body. 

 The high point of the gradient we will call the growth-centre. 



