496 
Bulletin No. 162.—1915. 
The distribution of frequencies with respect to time of hatching 
of both eggs is shown in Figure 5, the unbroken line connecting the 
records for the A-egg and the broken line those for B. The point of 
greatest interest which immediately impresses one on examining this 
figure is the remarkable extent to which the two polygons overlap, 
considering that there is a mean difference of slightly more than 44 
hours between the times of laying of the eggs whose hatchings are 
represented by the two polygons respectively. This fact is further 
brought out by considering the mean times of hatching of A and B, 
which, based on the 118 records for each, are 16.42 days for A and 
16.89 days for B, the time being reckoned in each case from the day 
on which B was laid.* In other words, we may say for practical 
purposes that although there is a mean difference of nearly two days 
in the laying of A and B, on the average A hatches 18.5 days after 
it is laid (16.5 days after B) and B hatches 17 days after its is laid. 
Table VI. — Correlation between hatching of first and second eggs. 
*In addition to the 118 records used above there are 13 in which the time of hatching of A is 
known, but not that of B, and in 18 cases the time of hatching of B alone is recorded. If these are 
included the mean for A is not changed, but that for B becomes 16.91. 
