196 
Journal o f Agricultural Research 
Vol. XXIX, No. 4 
of each of 45 pullets, while the case in 
which there was a difference in the 
mean weights of eggs producing the 
two sexes was with eggs laid during the 
normal hatching season. 
In view of the apparently different 
results obtained in the latter case, it 
was thought advisable to make addi¬ 
tional studies, particularly with eggs 
laid during the normal hatching season. 
EGG SHAPE IN RELATION TO CHICK 
SEX 
The eggs of 24 Barred Plymouth 
Rock pullets laid between the middle 
of February and the last of April were 
measured carefully at the time of lay¬ 
ing. The length and maximum 
breadth of each of 990 eggs were 
measured in millimeters, the measure¬ 
ments being recorded to hundredths of 
a millimeter. The sex of the chicks 
was determined by dissection at hatch¬ 
ing time. 
In Table I is shown the frequency 
distribution in terms of length in milli¬ 
meters of the eggs producing males and 
those producing females. Of the 990 
eggs, 512 produced males and 478 pro¬ 
duced females. The mean length of 
the eggs producing males is 55.31 ± 0.06 
mm. and the mean length of the eggs 
producing females is 55.42 ±0.07 mm. 
The eggs producing females have a mean 
length slightly greater than that of the 
eggs producing males, but the difference 
is not at all significant since it is only 
0.11 ±0.09, as shown in Table VIII. 
The variation in length, both absolutely 
and relatively, is quite small in each 
group of eggs producing males and fe¬ 
males. In Table II the production of 
each pullet is considered separately and 
there is not a single case in which the 
mean length of eggs producing males and 
those producing females is significantly 
different. Moreover, among the 24 
pullets there are 13 in which the mean 
length of eggs producing males is 
greater than the mean length of eggs 
producing females and 11 in which the 
reverse is the case. It can be said, 
therefore, that there is no relation be¬ 
tween length of egg and the sex of the 
chick hatched from it. 
The shape of an egg is determined 
by considering the length and breadth 
in relation to each other. The length- 
breadth index was used as a measure of 
shape and was obtained by dividing 
one hundred times the breadth by the 
length. A long and narrow egg has a 
relatively low index, while a short and 
broad egg has a high index. Based on 
the assumption that long eggs usually 
produce a preponderance of males, it 
should be expected that eggs producing 
males would have a lower index than 
eggs producing females. The fre¬ 
quency distribution of shape index and 
the relative mean indexes of eggs pro¬ 
ducing males and females, respectively, 
are shown in Table III. The mean 
index of eggs producing males is 
75.17 ±0.09 and the mean index of eggs 
producing females is 75.09 ±0.10, the 
difference with its probable error being 
0.08 ±0.13, as shown in Table VIII. 
There is very little difference in re¬ 
spect to the relative and absolute 
amounts of variability between the 
groups of eggs producing the two sexes. 
In Table IV the mean indexes of eggs 
producing males and females, respec¬ 
tively, are shown for each pullet and in 
no case is the difference in the mean 
index significant. It is apparent, there¬ 
fore, that there is no correlation be¬ 
tween the relative length of an egg and 
the sex of the chick hatched from it. 
In other words, long and narrow eggs 
having relatively low indexes as com¬ 
pared with short, broad ones, are not 
likely to produce male chicks in any 
greater proportion than eggs with 
relatively high indexes. 
EGG WEIGHT IN RELATION TO 
CHICK SEX 
Eggs from two different sources were 
used in this study of egg weight in re¬ 
lation to the sex of chicks. In the first 
case eggs were obtained from 153 
Barred Plymouth Rock females mated 
to Rhode Island Red males and in the 
second case from 58 Rhode Island Red 
females mated to Rhode Island Red 
males. The weights of 418 and 226 
eggs in the former and latter cases, re¬ 
spectively, are taken into consideration, 
making a total of 644 eggs. The eggs 
were weighed daily as laid, the weights 
being recorded to hundredths of a gram. 
