34 



VARIATION AND CORRELATION IN THE CRAYFISH. 



Table 17. 

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



Putting our results together we see that (a) in the case of meripo- 

 dites the influence of homology outweighs that of contiguity of parts; 

 (6) in the case of carpopodites the positional (contiguity) influence is 

 the greater; and finally (c) in the case of propodites there is a fairly 

 even balance between the two factors. Clearly it is impossible to lay 

 down any rule that in general the morphological relationship implied 

 in homology has a stronger influence in determining degree of correla- 

 tion between parts than does the relative position of the parts in the 

 organism (contiguity or separation). It would appear rather that relative 

 position of parts and homology are about equally efiFective in influencing 

 correlation. The important point, however, is that the influence of both 

 these factors is very slight. Our results indicate that both position and 

 homology are factors having a real influence on degree of correlation, but 

 the amount of these influences might, on general grounds, very easily 

 be — in fact probably has been — overrated. 



