990 Journal of Agricultural Research vol. vi.no. 2S 



most variable class of dwarf eggs is apparently those which have some 

 free yolk, while the yolkless dwarf eggs are more variable than the small- 

 yolked dwarf eggs — that is, the small-yolked dwarf egg approaches the 

 normal in degree of variability as well as in size and shape. In comparing 

 classes where the absolute difference in size is as great as it is between 

 normal and dwarf eggs the coefficients of variation are more accurate 

 measures of relative variability than are the standard deviations. In 

 order to determine whether or not the apparent difference in degree of 

 variability shown by the several classes is significant, it is necessary to 

 compare these differences with their probable errors. The second section 

 of Table V shows these differences in the size characters with their prob- 

 able errors and the ratio of each difference to its probable error. From 

 this table we see, first, that normal eggs are significantly less variable than 

 the least variable class of dwarf eggs (small-yolked dwarf eggs) in length, 

 breadth, egg weight, yolk weight, and probably shell weight. The sig- 

 nificance of the smaller variation in albumen weight is doubtful. Second, 

 small-yolked dwarf eggs are almost certainly less variable than other 

 dwarf eggs in length and probably also in weight. The significance of the 

 smaller variation in breadth is doubtful. . Third, the somewhat greater 

 variation in every size character in the dwarf eggs with free yolk than in 

 the yolkless eggs is not certainly significant — that is, it may be due to 

 errors in sampling. 



As previously stated, the coefficient of variation of index, which is a 

 percentage character, has no physical meaning. Since the index equals 

 the percentage that the breadth is of the length, all the indices are 

 measured in the same units and have the same possibilities of variation 

 in range. There is, then, less objection to comparing the standard 

 deviations of such a character; in fact, such a comparison is the only 

 available measure of the relative variability in shape of the several 

 groups. However, too much reliance should not be placed on the figures. 

 The differences in the standard deviations of the indices for the different 

 groups are as follows : 



Free-yolked — yolkless dwarf =o. 35±o. 40 



Yolkless — small yolked dwarf =1. 55 ± . 52 



Small-yolked dwarf — normal = . 62 ± .43 



The only deviation which can be considered of even probable signifi- 

 cance is the difference between yolkless and small-yolked dwarf eggs — 

 that is, normal eggs and small-yolked dwarf eggs are probably less 

 variable in shape than dwarf eggs without a formed yolk. 



The relative variability of the size characters within each group is also 

 of some interest. From Table IV it may be seen that the order of vari- 

 ability of the size characters of the egg is the same in normal eggs and 

 in each class of the dwarf eggs. The size characters arranged in the 

 order of their variability from most to least variable are (1) egg weight, 



