INTENSITY IN DIFFERENT PLANES OF SPACE 99 



a good approximation to constant differential growth-ratio ; 

 this exists also in the males' second phase, with a slight 

 falling off in the last point. The male chela shows positive 

 heterogony in both phases. In the female, there is a pro- 

 gressive falling off in the growth-coefficient during the second 

 phase, more marked for breadth than for length. The female 

 chela is positively heterogonic in the first, negatively hetero- 

 genic in the second phase. If the growth-coefficients are 

 calculated for the whole of the first phase, and between the 

 first and third points of the second phase, we obtain the 

 following result : 



TABLE XI 



Growth-coefficients for Length and Breadth of Chela in 

 Upogebia littoralis, calculated from the data of Tucker, 

 1930 



I.e. the ratio of growth-intensity for breadth to that for length 

 remains the same within the limits of experimental error so 

 long as the chela is positively heterogonic. When, however, 

 as in the females' second phase, it becomes negatively hetero- 

 gonic, the situation is reversed, and growth-intensity for 

 breadth falls below that for length. This reversal would 

 appear to be analogous to the reversal of sign of the growth- 

 gradients in negatively heterogonic organs (p. 87). Logarith- 

 mic plots (see Fig. 55) as well as Tucker's graphs indicate 

 some interesting points with regard to the action of the para- 

 site upon chela growth. The parasite has a general feminizing 

 action, very similar to that of Sacculina. In males, the effect 

 in reducing the growth-coefficient of chela-length is slight up 

 to 10-5 mm. carapace-length, for chela-breadth up to 8 mm. 

 carapace-length. From then on the growth-coefficient for 

 length remains just above that for females throughout ; that 

 for breadth, after approximating closely to that for females 

 until the second phase, fails to be as much reduced as the 



