Sex Ratios in Pigeons. 
495 
within an hour or two, but for the night we seldom known the actual 
time of hatching closer than that it occurred between 6 or 8 P. M. and 8 
A. M. It seems best therefore simply to group the hatchings into half¬ 
day classes, the one including the daytime period from 8 A. M. to 8 
P. M., the other the nighttime from 8 P. M. to 8 o ’clock the following 
morning.* By this method an egg hatching between 8 o’clock in 
the morning and 8 o 'clock in the evening of the seventeenth day after 
the laying of egg B would be put in class u 17;” if it was not hatched 
by 8 P. M., but was found out o° the shell at 8 o’clock the next morn¬ 
ing (that is, on the eighteenth day) it would be put into the “ 17.5” 
class. As has already been stated (p. 486) one of the eggs was often 
put into the incubator a short time before hatching, and hatched 
there, but there is no reason to believe that this has had an appreciable 
effect on the results. 
I1U. 1VCO ouuniug, «-- 
laving of the second egg. Solid line, first egg; dotted line, second egg. 
*As a matter of fact observations in many cases were not made after 6 P. M. Tabulations on 
this basis and on the 8 to 8 basis, show however practically no difference so far as our records 
indicate and it has accordingly seemed best to make the two classes of equal length. It should be 
remembered, however, that in an unknown proportion of the cases the night period is in reality 
longer than the day period. This may account in part for the larger number of recorded hatchings 
at night (see p. 497). 
