24 



VARIATION AND CORRELATION IN THE CRAYFISH. 



In his study of correlation in Gelasimus pugilator Duncker (1903) 



finds evidence of a law of contiguity. He says (p. 319): 



Der wie bei bilateral homologen Merkmalen uberhaupt Btets positive Korrela- 

 tionskoeffizient der untersuchten Paare homologer Dimensionen ist um so grosser, je 

 nSher die gemessenen Organe einander liegen. 



With our present material it is obvious that we may consider the ques- 

 tion of contiguity and correlation from two standpoints. First, we may 

 take the structures in contiguous or non-contiguous metameres, i. e., in 

 the antero-posterior series; and again, we may test the matter on the con- 

 tiguous and non-contiguous segments within the single metamere. This 

 last gives what may be called a lateral series. 



Taking first the location of parts in successive metameres, table 9 

 has been arranged to bring together the results in most convenient form 

 for direct comparison. Since we have data from three legs, it is evident 

 that there are three possible combinations of pairs, viz, i with ii, i with 

 III, and II with ill. In the second, third, and fourth vertical columns of 

 the table the correlation coefficients for the joints of these three combina- 

 tions of legs are given. The particular pair of joints to which an indi- 

 vidual coefficient belongs is given in the first column of the table. The 

 first joint of each pair as they are entered in this column always belongs 

 to the first leg of each of the three pairs at the heads of the columns. 

 Thus, to take a single example to illustrate how the table is to be read, 

 by looking at the point where the sixth row and the second column of 

 figures meet, the entry 0.9601 is seen; this is the coefficient measuring 

 the correlation between the carpopodite of the cheliped and the meripodite 

 of the second walking leg. Finally, in the last column of the table a plus 

 sign ( + ) is entered whenever the correlation between a contiguous pair 

 of legs is greater than the correlation between a non-contiguous pair. 

 When the correlation is greater for a non -contiguous pair a minus sign 

 ( — ) is entered. 



Table 9. — Correlation and location of segments. 



