No. 3.] VARIATION IN THE TEETH OF NEREIS. 



From the table of frequencies it will be seen that the num- 

 ber of definite teeth varies from I to 8, the indefinite from 

 i to 9, the total numbers from 5 to 14. 



The following constants were obtained. 



II. TABLE OF CONSTANTS. 



Comparison of these numerical results suggests the follow- 

 ing conclusions : 



The mode, 5, is the same for the definite and indefinite on 

 both sides, and for the total on each side it is 10. The aver- 

 ages also show little difference between the right and left jaws. 

 From the variability, however, as indicated by the standard 

 deviation, it appears that the number of teeth of the right jaw 

 is slightly more variable than that of the left, cr being 0.074 

 greater on the right side for the definite teeth, o.on (which 

 is less than the probable error) for the indefinite teeth, and 

 0.033 greater for the right total. The highest degree of varia- 

 tion is shown by the total number of teeth on the right side, 

 and the least variation is shown by the number of indefinite 

 teeth. 



The form of the distribution curve of definite teeth on both 

 jaws falls under Pearson's Type I, with the peculiar result of 

 a slight negative skewness for the left side, and a positive 

 skewness, although a very slight one, +0.0153, for the right. 

 This indicates a tendency to the production of fewer definite 

 teeth than normal on the left side, and a faint tendency 

 towards a greater number on the right side. The distribution 

 curve of indefinite teeth on both sides is of Type IV, with a 

 negative skewness, 0.043, on tne l 6 ^ side, anc ^ twice this, 

 0.086, on the right ; i.e., there is on the right side a greater 



