580 



THE AMERICAN NATURALIST [Vol. XLIV 



and Vineyard Sound conform quite closely with respect 

 to their arithmetical means to the standards above men- 

 tioned. 



6. Time and Place Factors Compared. — When a com- 

 parison of the standard deviation of these 1899 shells is 

 made to ascertain whether the greater variability is as- 

 sociated with time (due to inherent germinal modifica- 

 tions), or with place (associated with environmental 

 modifications), it appears that while time is rather the 

 more important factor, yet the result is not uniform and 

 convincing. This comparison is shown in Table VI, in 

 which the difference between the standard deviation of 

 the July shells of each locality with the July 5 shells of 

 three other localities is obtained to indicate differences 

 due to place, and second, the difference between stand- 

 ard deviation of the July 5 shells in each locality and 

 those of July 21 and August 5 for the corresponding lo- 

 cality are reckoned to show the effect of time. 



TABLE VI 



In Table VI, if we first consider the case of the Nobska 

 Point shells in the top line of the table and utilize those 

 collected upon July 5 as a standard for comparison it ap- 

 pears that shells from the same locality but collected two 

 and four weeks later show a greater difference in varia- 

 bility (standard deviation) than shells collected from any 

 of the three other neighboring localities upon the same 

 date of July 5. That is, the factors dependent upon time 



