32 



VARIATION AND CORRELATION IN THE CRAYFISH. 



From table 15 it would appear that, so far as meripodite correlations 

 are concerned, there is a distinct tendency for homologous joints of two 

 different legs to be more highly correlated together than are the different 

 joints of the same leg, whether contiguous or not. There are only three 

 exceptions to the rule, and in these cases the differences are insignificant 

 in comparison with their probable errors (cf. excess column). 



Table 15. 

 (A) MERIPODITES OF LEGS I AND II, AND II AND III (CONTIGUOUS METAMERES). 



Homologous 



JoiffTS. 



Meripodite i 

 with meripo- 

 dite II {aa' ). 



Meripodite ii ^ 

 with meripo [• 

 dite III {aa"). ) 



Coefficient. 



0.9665 ± 0.0026 



.9729 ± .0021 



Excess. 



+ ( 1.88) 

 + ( 7.76) 

 + ( 4.43) 

 -( 0.89) 

 + ( 8.85) 

 + (10.18) 

 + ( 1.06) 

 -( 0.23) 



Coefficient. 



0.9588 

 .9083 

 .9439 

 .9696 

 .9083 

 .8742 

 .9696 

 .9736 



± 0.0032 



± .0070 



± .0044 



± .0024 



± .0070 



± .0095 



± .0024 



± .0021 



Non-homologous 

 Joints of same Leg. 



Meripodite i with car- 



popodite I (ab). 

 Meripodite ii with car- 



popodite II {a'b' ). 

 Meripodite i with 



propodite i (ac). 

 Meripodite ii (with 



propodite ii (a' c' ). 

 Meripodite ii with car- 



popodite III {a'b'). 

 Meripodite iii with car- 



popodite III (a "6"). 

 Meripodite ii with 



propodite ii {a'c' ). 

 Meripodite iii with 



propodite iii {a" c"). 



(B) MERIPODITES OF LEGS I AND III (NON-CONTIGUOUS METAMERES). 





Meripodite i 

 with meripo- 

 dite III {aa"). 



0.9686 ± 0.0025 



+ ( 2.39) 

 + { 9.63) 

 + ( 4.84) 

 -( 1.52) 



Meripodite i with car- 

 popodite I {ab). 



Meripodite iii with car- 

 popodite III (a "6"). 



Meripodite i with pro- 

 podite I («c). 



Meripodite iii with 

 propodite iii {a"c"). 



Table 16 demonstrates that in the case of the carpopodites, on the 

 whole, the contiguous joints of the same leg are more highly correlated 

 than homologous joints of different legs. In only three cases out of twelve 

 is the excess in favor of the homologous joints, and in those cases the 

 differences are relatively small. The carpopodite correlations thus show 

 exactly the reversed relation to what the meripodite correlations do, 

 though the differences, as shown by the ratios in the excess column, 

 are relatively smaller than in the former case. 



