686 
Journal of Agricultural Research 
Vol. XXXI, No 7 
and hatching quality of eggs laid by a flock of Barred Plymouth 
Rock pullets has also been considered, and the data pertaining there¬ 
to are presented here. 
MATERIAL AND METHODS 
The group of birds on which the study of the relationship between 
egg shape and hatching quality is based consisted of two flocks each 
of 12 Barred Plymouth Rock pullets mated to Brown Leghorn cock¬ 
erels. The eggs laid between the first of February and the last of 
April were dated and carefully measured when laid. The length and 
maximum breadth of each egg were measured in millimeters, the 
measurements being recorded to hundredths of a millimeter. The 
length-breadth index was used as a measure of shape and was obtained 
by dividing 100 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. 
Five groups of birds contributed the material for the study of the 
relationship between egg weight and hatching quality. The first 
S oup consisted of 53 Rhode Island Red hens mated to Rhode Island 
ed cockerels. The second group consisted of 30 Rhode Island Red 
pullets mated to Rhode Island Red cockerels. The third group 
consisted of 50 Barred Plymouth Rock hens mated to Rhode Island 
Red cockerels. The fourth group consisted of 113 Barred Plymouth 
Rock pullets mated to Rhode Island Red cockerels. In the case of 
each of these groups, matings consisted of from 12 to 15 females mated 
to one haale. The fifth group consisted of the two matings of Barred 
Plymouth Rock pullets with the Brown Leghorn males mentioned. 
In the case of the first two groups the eggs were laid between March 5 
and March 23; the eggs of the second two groups were laid between 
March 15 and March 23; the eggs of the last group were laid between 
the first of February and the last of April. The eggs were dated and 
weighed daily as laid, the weights being recorded to hundredths of a 
gram. 
The eggs of the four largest groups of birds were incubated in a 
triple-deck mammoth incubator, 5,400-egg capacity, the conditions 
of the incubation for all the eggs being kept as nearly uniform as 
possible. The eggs of the fifth group of birds were incubated in an 
electric incubator of 100-egg capacity, the conditions of incubation 
also being kept as nearly uniform as possible. All eggs were tested on 
the seventh day, records being made of the infertile ones and those in 
which the embryo had died. A second test was made on the fifteenth 
day, records being made of the embryos which died between the 
seventh and fifteenth days. On the nineteenth day of incubation the 
eggs were removed from the incubators, and each egg was placed in a 
separate hatching sack and replaced in the incubator. On the 
twenty-second day all hatching sacks were removed from the incu¬ 
bator, and the eggs which hatched were recorded as well as those in 
which the embryo had died between the fifteenth and the twenty- 
first days. 
In the tables which follow, the data for embryo mortality are divided 
into two parts, embryos which “died early” and embryos which 
“died late.” The embryos recorded as having died early include all 
