Sex Ratios in Pigeons. 
491 
standard deviation is slightly, though scarcely significantly, greater 
than the variability in the times of laying of A and B respectively 
(or =1.120 + 0.079). 
Table IV .—Interval bctiveen laying of eggs A and B arranged by months. ( In¬ 
cludes 89 records made in 1898.) 
Perhaps the most interesting fact with respect to the interval 
between the laying of A and B comes out when the records are con¬ 
sidered by months, as is done in Table IV. The 12 records of 1907, 
which were scattered throughout the year, are not included in this 
table. A comparison of the means for the different months shows that 
with the exception of January, for which there was but a single record, 
and which may therefore be disregarded, the mean time between 
the laying of A and B decreases perceptibly for each month from 
February to July. This fact is shown more graphically in Figure 4, 
where the means are plotted with their values as ordinates and the 
months as abscissae. The straight line which best fits these obser¬ 
vations has the equation y = 46.02 - 0.385x, where y is the in¬ 
terval between the eggs in hours and x the month of the year from 
February to July, inclusive. 
