SUMMARY AND CONCLUSIONS. 47 



(8) The evidence as a whole points to the conclusion that homology 

 is a factor of relatively very slight importance in determining degree of 

 correlation between parts. In the case of certain joints of the legs (the 

 meripodites) homologous joint pairs are significantly more highly corre- 

 lated together than are non-homologous joints. Such a relation does not 

 hold uniformly for all joints, however, and, furthermore, in the cases where 

 it does obtain the differences between homologous and non-homologous 

 joint pairs in respect to degree of intercorrelation are absolutely very 

 small. The results indicate that, as compared with physiological factors, 

 morphological relationship is, for practical purposes, a factor of negligible 

 significance in influencing degree of correlation between parts. 



(9) A study of the partial correlations between the joints of the legs 

 when the cephalothorax length is kept constant leads to the conclusion 

 that a very considerable part of the gross observed correlations between 

 the different segments of the legs arises through the high correlation 

 between the size of these segments and the size of the body as a whole. 

 In other words, it appears that the degree of gross correlation between 

 parts in the crayfish is in each case the resultant of two sets of influences. 

 There is first a general growth correlation factor which accounts for a 

 considerable part, but not all, of the observed gross correlation. Besides 

 this growth correlation sensu strictu, there is left a portion of the gross 

 correlation, to account for which other physiological factors must be 

 adduced. In the analysis of these factors by experimental investigation 

 lies the hope of progress in the problem of the origin of organic correlation. 



(10) The data show that in the crayfish there is in general a substan- 

 tial degree of correlation between the proportionality of the parts and the 

 absolute size of the organism. We are thus able to add one more to the 

 list of organisms in which this relationship has been shown by quantita- 

 tive methods to be true. The bearing of this result on certain of Driesch's 

 theoretical deductions regarding a vitalistic hypothesis is discussed. 



