Sex Ratios in Pigeons. 
503 
of the time of incubation,” and “will frequently incubate infertile 
eggs until completely exhausted, if no one takes the trouble to stop 
her. ” 
Anyone who has had even a little experience raising pigeons 
well knows that RaspiaPs generalization with regard to their always 
abandoning their eggs on the eighteenth day in case they do not 
hatch is unfounded and unjustified. Wright (1879, p. 40) observes 
incidentally on this point: “We have occasionally kept birds we 
desired as feeders as much as seven days on eggs (in one case eleven 
days) beyond the proper time of hatching, and then given them young 
ones only two days old. ” 
Even before we knew of Raspial’s papers we had begun the collec¬ 
tion of records relating to the time the birds would continue to 
incubate the eggs in case they did not hatch. Most of the records 
were made from sets in which the eggs were sterile or in which the 
embryos died, but in a few cases the eggs were boiled to prevent their 
hatching, in order that more data on this point might be obtained. 
In some cases one of the eggs became broken or was otherwise lost 
during the course of the incubating process; it was then either re¬ 
placed by a sterile “ dummy” egg, or the birds were allowed to con¬ 
tinue with the one egg only. In one or two instances one egg hatched, 
but the squab dying very soon the birds continued incubating the 
other. Although the records thus represent a variety of conditions, 
they are all cases in which the birds had incubated normally the full 
17 days, and there therefore seems to be sufficient uniformity in the 
conditions influencing their behavior to allow of their all being 
treated together as is done in Table VIII. From the footnotes 
appended to the table it is seen that certain factors, such, for example, 
as the cases in which no second egg was laid, which might be con¬ 
ceived to have an influence on the time of sitting, are distributed 
through the records with impartial uniformity. 
The 59 matings included in the table are all for the earlier years of 
our work (1908-1910); since that time the change of method in using 
foster parents for raising the young of selected parents and the forcing 
