216 CERTAIN LAWS OF VARIATION. 



cent, greater). The variability is in every case con- 

 siderably greater for the American shells, as Bumpus 

 had concluded. The average variability of all the 

 American samples is 2.765, or 18.2 per cent, larger 

 than the average for the British (2.34). 



LOCALITY. MEAN. VARIABILITY. 



I. f Tenby, Wales, . . . .90.96 2.38 



II. \ South Kincardineshire, Scotland, 87.85 2.34 



III. [Huinber District, . . .90.53 2.30 



IV. St. Croix River, Maine, . .91.26 2.70 

 V. Casco Bay, Maine, . . .92.53 2.67 



VI. Beverly, Mass., . . . .90.65 2.76 



VII. Nahant, Mass., . . . .92.19 3.03 



VIII. Plymouth, Mass., . . .90.09 2.48 



IX. Seaconnet, R. I., . . .89.72 2.86 



X. Newport, R. I., . . . . 89.17 2.62 



XI. Bristol, R. I. (shingle), . .90.77 2.75 



XII. Bristol, R. I. (sand), . . . 91.07 2.83 



XIII. Warren River, R. I. . . .92.69 2.95 



Bumpus found that in other respects also the Ameri- 

 can shells are more variable than the British. Thus 

 they show greater variations of ventricosity in the 

 course of growth; shells of a given length exhibit a 

 greater range of variation in weight; also their colour 

 markings are more variable. Hence there can be no 

 doubt that the general variability of the organism has 

 increased. As in the case of the sparrow's egg, 

 Bumpus attributes this to its emancipation from many 

 of the restraining influences of Natural Selection; but 

 it seems to me a simpler explanation, as was suggested 

 in the case of the eggs, to regard the effects produced as 

 largely, if not entirely, the direct result of want of 

 adaptation to the changed and perhaps more variable 

 conditions of life. 



