Apr. 19,1924 Relation of Antecedent Egg Production to Sex Ratio 211 
weight and sex ratio, and this is hardly to be expected, particularly in view of the 
fact that over 60 per cent of the absolute weight of the egg constitutes albumen 
and shell, both secreted around the yolk subsequent to maturation and fertiliza¬ 
tion. 
5. THE RELATION OF YOLK WEIGHT TO SEX RATIO 
Since the yolk is a single cell and since the earliest stages of embryonic develop¬ 
ment take place during the absorption of yolk granules in the growth of the ovum, 
it is well to inquire if the yolk weight bears any relation to the sex ratio. In 
order to study this point the weights of the eggs and their yolks laid by seven 
Barred Plymouth Rock hens of the poultry flock of Macdonald College were 
determined daily throughout one year of production. These weights are shown 
in Table IX, along with the sex ratios, for the production classes as shown pre¬ 
viously, except that the sixth class is not represented owing to the limited number 
of eggs produced. 
Table IX .—Showing the relation between yolk weight and sex ratio 
Class 
Produc¬ 
tion 
Average 
wlfjbt 
Average 
yolk 
weight 
Sex ratio 
1... 
0-20 
21-40 
41-60 
61-80 
81-100 
Grams 
46.33 ±0.31 
50.07±0.34 
52.40±0.41 
51.08 ±0.68 
49.16±0.34 
Grams 
15.13±0.23 
15.34±0.26 
15.92 ±0.28 
15.89±0.27 
15.34±0.26 
62.91 ±1.44 
57.46±1.88 
45.00±2.04 
44.61 ±0.69 
37.65±1.00 
2..... 
3... 
4..... 
5___ 
It will be observed from Table IX that apparently there is a correlation be- 
between egg weight and yolk weight, the heavier the egg the heavier the yolk. 
This is a similar result to that observed by Atwood and Weakley, in ana¬ 
lyzing the egg records of a number of birds at the West Virginia Experiment 
Station. The relationship, demonstrated in this study, existing between egg 
weight and yolk weight, is in close agreement with the results of Atwood and 
Weakley, but is in disagreement with the results observed by Riddle (46, 47) 
with pigeons. In a generic cross between Turtur orientalis and Streptopelia alba, 
the cross most largely studied, Riddle makes certain observations regarding yolk 
weight. 
The result clearly establishes the fact that the yolks of late summer and autumn—those that produce 
mostly, or ah, females—are larger than the yolks produced in the spring which give rise to males” (46, p. 
889). “The balances alone and at once showed that the mass of the yolk of the first egg of nearly all pairs 
of eggs (from pure species) was less by from (usually) 9 per cent to 15 per cent than the mass of the yolk of 
the second egg of the pair (47, p. 380). 
In regard to the first statement, the results of this study show that in the 
domestic fowl the yolk weight tends to increase slightly up to a production of 
about 60 eggs, after which it decreases. This is the same general trend followed 
by egg weight, and since there is no significant difference in the weights of eggs 
giving rise to females and males, respectively, it does not seem probable that there 
is any correlation between yolk weight and sex ratio. In regard to Riddle’s 
second statement, it should be observed that the “mass” of yolk in the egg 
producing a male pigeon is reported to be usually from 9 to 15 per cent less 
than the “mass” of the yolk producing a female whereas in the domestic fowl 
there is no such indication of a differential yolk weight situation. Concerning 
yolk weights in the domestic fowl, Atwood and Weakley ( 1, p. 85) make the 
following observation: “When eggs are laid in cycles, the first egg in the cycle 
is usually the heaviest, the other eggs decreasing in weight according to their 
position in the cycle. The weight of the yolk decreases according to the position 
