202 



MICHIGAN ACADEMY OF SCIENCE. 



r=— .629. 



This result is of considerable interest, since it shows that as the num- 

 ber of somites in front of the clitellum increases there is a strongly 

 marked tendency for the number of somites in the clitellum to decrease. 



The possible signiflcance of the normal existence of negative correla- 

 tion for problems of morphogenesis was discussed. The suggestion was 

 made that possibly negative correlation might have ultimately the same 

 physiological basis as compensatory regulaiion. 



The value for the coefficient of correlation between total length and 

 total number of somites in the earthworm was found to be 



r =.2()(). 



This indicates a rather low degree of correlation between these char- 

 acters. 



The complete paper, of which this is an abstract, will appear in an- 

 other place. 



VARIATION AND CORRELATION IN ARCELLA. 



RAY.AIOND PEARL AND FRANCIS J. DUNBAR. 



(Abstract.) 



The results of a statistical study of the variation of the shell of the 

 common Arcella ndgaris with respect to the following characters were 

 presented: (a) Total diameter of shell (=''outer diameter"), (b) diam- 

 eter of opening in shell (="inner diameter"), (c) color of shell. 



The constants of the frequency distributions for outer and inner diam- 

 eters are given in the following table : 



