218 
Journal of Agricultural Research 
Vol. XXVIII, No. 3 
ence in size between male and female producing spermatozoa in the rabbit. 
The explanation offered will not hold for the domestic fowl, however, where the 
male is homozygous for the sex character. If there is selective fertilization, from 
the standpoint of male-producing or female-producing eggs being more readily 
fertilized under certain conditions, the only tenable explanation would seem to 
lie in some causes affecting the maturation of the egg, 
5. SEX DETERMINATION PRIOR TO FERTILIZATION 
Apparently a solution of the problem concerning modifications in the normal 
sex ratio in the domestic fowd belongs to the domain of gamete development. 
It has been shown that sex is apparently not reversible during embryonic devel¬ 
opment and, furthermore, that sex is probably determined at the time of fertiliza¬ 
tion. Deviations from approximate equality of the number of males and females 
must be interpreted in terms of influences affecting the development of the 
gametes which subsequently take part in the process of fertilization. 
Along this line must first be mentioned the possibility of differential matura¬ 
tion, since it has already been observed that during the early period of egg pro¬ 
duction the actual number of male-producing zygotes exceeds the actual number 
of female-producing zygotes, and that as egg production increases the situation 
tends to be reversed. The possibility of the existence of differential maturation 
has been shown to exist in some forms of insects. In the case of the currant 
moth, Abraxas grossulariata, Doncaster ( 12 ) bred seven generations of a strain 
of Abraxas in which some broods in each generation were all females. Don¬ 
caster (12, p. 132) suggests the possibility that “in these families all of the eggs 
have a tendency to extrude the male-determirfing sex chromosome, just as in 
aphids the male-producing eggs all extrude the female-producing X chromosome.” 
In Talaeoporia tubulosa, Seiler (49) has shown that in the anaphase of the first 
polar division the unpaired X chromosome seems to go into the polar body 
rather more frequently than into the oocyte nucleus. In this species females 
are more numerous than males, so that genetic and cytological facts are in agree¬ 
ment. 
Might a simliar condition exist in the case of the domestic fowl? The process 
of maturation begins in the fully ripe follicle and is completed after ovulation. 
At the time of ovulation the first maturation spindle is still in the equatorial 
plate stage, the outer end of the spindle being in almost immediate contact with 
the surface of the ovum. The first polar body is thrown off and almost immedi¬ 
ately the second maturation spindle is formed. The position of the second 
maturation spindle is similar to that of the first, and a second polar body is 
thrown off. Whichever maturation division serves as the reduction division 
must also serve in the elimination of a greater number of female-producing 
than male-producing complexes during the early period of egg production and 
the elimination of a greater number of male-producing than female-producing 
complexes during the later periods of egg production, if this is the explanation 
of the results obtained. During the normal hatching season there would seem 
to be no influence at work affecting the apparent chance elimination of either 
kind of complex. Is there any evidence concerning the selective elimination of 
complexes of a particular kind? Heape (26) has thus interpreted his results 
with canaries bred under different conditions. He found that certain conditions 
affected the sex ratio, and he assumed that under conditions of early breeding 
and light feeding male-producing gametes are produced in excess, while undei 
conditions of late breeding and heavy feeding female-producing gametes art 
produced in excess. Heape’s results are similar in nature to those secured by 
