202 
Journal of Agricultural Research 
Voi. XXVIII, No. 3 
1. THE NORMAL SEX RATIO 
The term “normal sex ratio” is understood to mean the sex ratio obtained dur¬ 
ing the normal hatching season, which may be considered to include approximately 
the months of March and April. 
Pearl (4-4) 3 has indicated the advantages, from a methodological viewpoint, of 
treating sex-ratio data from the standpoint of the family as the unit and, further¬ 
more, he has shown quite clearly that the value of the male ratio, based on fam¬ 
ilies of 10 or more “is much nearer the true biological norm” than values based 
upon the population as a whole and on families of less than 10. For instance, he 
obtained the following ratios: Families of all sizes, Rc? =49.45; families of from 
one to three Ref =55.07±2.11; families of from four to nine, R<f —49.39±0.84; 
families of 10 or more, Ref =48.57±0.28. Pearl has shown that size of family 
has an obvious influence on the sex ratio, and he also points out that “families 
under 10 can not be considered as representative of the normal fertility of the 
domestic fowl.” 
Taking Pearl’s basis as the correct one on which to determine the mean sex 
ratio of the domestic fowl for portions of the annual production, and assuming 
that the value 48.57 ±0.28 was obtained for the normal hatching season, which 
in the State of Maine would include approximately the months of March and 
April, the data in this study have been arranged to show the mean sex ratio for 
the months of March and April and for the preceding and subsequent seasons of 
production, all ratios being computed on the basis of families of 10 or more. 
Table II.— -Showing the mean sex ratio for the normal hatching season and for the 
preceding and subsequent seasons of production. Based on families of 10 or more 
Period No. 
Year 
Females 
i 
Males 
Sex ratio 
! 
I (from the commencement of laying to the end of 
February)_ 
[1919-20 
-{1920-21 
(1921-22 
108 
68 
177 
160 
89 
198 
59.70±1.97 
56.69±1.53 
52.80dbl. 18 
Total....... 
353 
447 
55.87±0.98 
II (normal hatching season, March and April) __ 
Total.-.. 
[1919-20 
-{1920-21 
[1921-22 
178 
87 
214 
160 
102 
195 
47.34db0.83 
53.97db2.16 
47.68±0.93 
479 
457 
48.82±0.80 
Ill (From the first of May to the end of October). 
Total...... 
/1919-20 
\1920-21 
247 
91 
142 
55 
36.50±0.86 
37.67±1.42 
338 
197 
36.82±0.61 
Differences 
I-II 
7.05=fcl. 22 
II-III 
12. OOdtl. 01 
I-III 
19.05±1.15 
It should be mentioned here that the sex ratios based on the population as a 
whole for each of the three periods shown in Table II have been found to be as 
follows: Period No. I, from the commencement of laying to the end of February, 
Rc? =55.95 ±1.70; Period No. II, normal hatching season, March and April, 
R d 1 =49.01 ±1.03; Period No. Ill, from the first of May to the end of October, 
Re? =36.93±0.87. When compared with the sex ratios determined for the same 
periods based on families of 10 or more, 55.87 ±0.98, 48.82 ±0.80, and 36.82 ±0.61, 
as shown in Table II, it is apparent that the values of the ratios based on families 
of 10 or more show less variability. 
From Table II it is evident that the sex ratio for the normal hatching season, 
Rc? =48.82 ±0.80, is comparable to the value, Rc? =48.57 ±0.28, as determined 
by Pearl. It should be remembered that Pearl was dealing with much larger 
numbers. The difference is not significant, however, since the difference with its 
probable error is 0.25 ±0.85. At the same time, it may be pointed out that this 
3 Reference is made by number (italic) to “ Literature cited," pp. 221-224, 
