CORRELATION AND LOCATION OF PARTS. 23 



Summarizing the results of the section: It has been shown that in 

 the system of organs given by the joints of the crayfish leg, the most 

 highly differentiated and specialized organ of those studied, the great 

 chela, exhibits the greatest amount of variation and the highest degree 

 of skewness in its variation. Aside from the great chela the most vari- 

 able single segment on each leg is the carpopodite. This joint also shows 

 the greatest skewness in its distributions. In the cases where the differ- 

 entiation between segments is not very great in amount, there is very 

 little difference in the relative variabilities. So far as our variation 

 results go they suggest the following conclusions: 



(i) That relative degree of morphological development or specializa- 

 tion and relative degree of variability run parallel. 



(ii) That degree of skewness and degree of variation tend to run 

 parallel. 



It is to be understood that these are only the statements of results 

 obtained from the present material. They are not offered as generaliza- 

 tions, but rather as suggestions of questions on which any additional data 

 will be welcome. 



CORRELATION AND LOCATION OF PARTS. 



The discussion of the correlation results may conveniently be begun 

 with the consideration of the problem of the influence of the relative 

 position of two organs on the correlation between them. Is the correla- 

 tion between two contiguous organs or parts in general greater than the 

 correlation between two organs more or less widely separated from one 

 another? Or, put more generally, is there any definite relation between 

 degree of correlation and relative location of parts within the organism? 

 It is obvious that a definite answer to this question would be of impor- 

 tance in any attempt to formulate a general theory of the origin and laws 

 of organic correlation. In their elaborate study of the correlation between 

 the different bones of the human hand Lewenz and Whiteley (1902) found 

 in several instances clear evidence of such a "rule of neighbourhood," as 

 they term it. Thus they find (p. 360) that: 



Generally there is a "rule of neighbourhood," i. e., any bone is more closely cor- 

 related with a second of the same series than with any other from which it is separated 

 by that second. Speaking roundly this is true for both lateral and longitudinal series; 

 but there are apparently significant deviations from this rule, the most notable of which 

 are, perhaps, those of the distal phalanges, which on all of the fingers of both hands tend 

 to be more highly correlated with the metacarpal bones or the proximal phalanges than 

 with the middle phalanges. The middle phalanges, however, obey the general rule. 



