1895.] into the Measurable Characteristics of Plants, $c. 365 



FIGK 3. Distribution of Frontal Breadths in 8069 Female Crabs from Plymouth 

 Sound, old and young. Deviations expressed in terms of the Modulus. The 

 three cases of deviation greater than three times the Modulus are omitted. 



deviations and that indicated by the probability integral is fairly 

 close. The mean error of the observed curve is 0'5621, whereas ih 

 should be I/ */Tr = 0'5642, the difference between the two figures bein^* 

 less than 0*5 per cent. The error of mean square is 0*7123, instead of 

 Q'7071, a difference of less than 1 per cent. The sum of the squares 

 of the positive deviations is 2115. The sum of the negative devia- 

 tions is 1992. The total number of individuals of deviation more than 

 O'l is 3593 on the positive, 3574 on the negative side, a difference 

 of about one-half per cent. 



On the whole it may be said that the result agrees with that given 

 by the theory of probability as well as could be expected from the 

 number of observations, and that the law of frequency of variation 

 throughout the series may, as was hoped, be assumed to agree with 

 the ordinary law of chance. 



From the result so far obtained it followed that a determination 

 of the quartile deviation, or any other of the constants of the pro- 



2 D 2 



