130 PROCEEDINGS OF THE AMERICAN ACADEMY. 



a small one on the other side. The side is indeterminate, about fifty per 

 cent of the individuals being right-handed and fifty per cent left-handed. 

 The great claw is nearly thrice as large as its fellow of the opposite side. 

 Nevertheless, the correlation is as high as in some cases of symmetrical 

 organ ; it is, namely, 0.774. 



In the case of Pecten opercularis from the Irish Sea the correlation 

 between the breadth of the right valve and that of the left valve is 

 r — 0.8578 + .0056. This correlation is higher than between some sym- 

 metrical organs in vertebrates and in the lower vertebrates. It is, how- 

 ever, lower than the symmetrical correlations in man. 



The question arises whether in the new position of a species the parts 

 arranged about the newly assumed vertical axis may not have a high 

 correlation. Duncker has found this to be the case in the flounder. 

 Thus the correlation between the dorsal and the ventral fin-rays is 0.672 ± 

 .011, so that the morphologically dissimilar but now antimerically placed 

 organs are more closely correlated in their variations than the bilaterally 

 homologous organs. The same thing is found in Pecten. In the normal 

 position of Pecten, in which it lies upon its right side, so that its trans- 

 verse axis is vertical, the antero-posterior and the dorso-ventral axes 

 are horizontal. What is the correlation between the lengths of these 

 horizontal axes? 



TABLE IV. 



Correlation Coefficients between the Antero-posterior Diameter and 

 the Dorso-ventral Diameter of the Lower Valve of Pecten Opercu- 

 laris from Three Localities. 



Locality. Number of Individuals. r. P. E. r. 



Eddystone (Appendix A) 537 0.96997 -L_ .00124 



Irish Sea (Appendix B) 613 0.97596 -J- .00093 



Firth of Forth (Appendix C) 507 0.98495 -±- .00063 



Here the correlation coefficients of non-bilateral dimensions are ex- 

 tremely high, as high as in many of the highest human coefficients 

 between bilateral dimensions. As a result of the newly assumed position 

 of the scallop, two formerly largely independent axes have come to vary 

 simultaneously just because they have similar relations to the bottom. 

 Pecten has gained a new kind of symmetry ; namely, a radial symmetry. 

 The fact points very forcibly to another conclusion ; namely, that physio- 

 logical factors are much more important in determining correlation than 

 morphological relationship when the two come in conflict. 



"We have considered the variation and correlation of the transverse 

 diameters of the two valves and also the correlation between dorso- 



