Sex Ratios in Pigeons. 
469 
Number 
of deaths. 
Days “ 0 5 10 15 20 25 30 35 40 45 50 
Q 
Fig. 1. Number of squabs dying at each day of age up to fifty days. D. i. s., dead in shell ’ 
0, day of hatching; 1, one day old; etc. 
In Figure 1 is represented the number of birds dying at each 
age, at one clay intervals, up to 50 days. In the “dead in shell” 
column only those embryos are included whose sex was determined. 
The number of fertile eggs which failed for one reason or another 
to hatch was, of course, very much larger. 
Since records are systematically taken once daily, the recorded 
age at death is usually correct within that period; in a comparatively 
small number of cases a bird may have been dead for a somewhat 
longer period before discovered, and there are included records of 
some birds which were killed because so sick it was evident they would 
not recover and that death would probably have intervened within 
a short time. These slight inaccuracies tend to offset one another, 
