.376 Report of the Committee for conducting Inquiries [Feb. 28, 



FIG. 6. Deviations of 8020 measures of Eight Dentary Margin in Female Crabs, 

 old and young, from Plymouth Sound, expressed in terms of the Modulus. 

 Eleven individuals of deviation greater than three times the Modulus are 

 omitted. 



vidual of deviation equal to 7 times the modulus, would make the 

 sum of the positive and negative squares almost exactly equal. 



The mean error of the whole system is 0'5688 instead of 0*5642, or 

 nearly 1 per cent, too great. The error of mean squares is 0*7276 

 instead of 0'7077, or 2'8 per cent, too great. 



From these ^alues of the mean error and error of mean square, 

 as well as from the presence of a deviation so great as seven times the 

 modulus, it is evident that some cause has been at work, producing 

 large abnormalities with a frequency greater than that indicated by 

 the theory of chance. Reference to the table shows that deviations 

 of more that 2' 5 times the modulus do in fact occur twenty times, 

 instead of five or six times, as they should do So that deviations of 

 this magnitude occur about three and a half times too often. 



The sporadic occurrence of considerable deviations, which do not 

 obey the general law of frequency of ' variation, is a phenomenon 



