Apr. 19,1924 Relatio n of Antecedent Egg Production to Sex Ratio 
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Pearl (45 ), Riddle (46, 47 ), Crew and Huxley (6 ), and the results secured in thie 
study, except that in the last four cases the method of feeding has" apparently 
had no influence, inasmuch as the birds were all fed similarly throughout the 
duration of the tests. In the case of the present study, then, if differential 
maturation occurred it must be accounted for as a result of conditions of egg 
production. That is, differential maturation must be looked upon as an effect, 
produced by certain conditions, the nature of which will be discussed presently. 
A very interesting case, bearing on the discussion as it has been developed up 
to the present, is reported in one of the forms closely related to the plant lice 
Phylloxera fallax . Morgan (36, 37) has shown that the sex of the individual 
developing from the parthenogenetic egg is determined before the distribution 
of sex chromosomes at polar body formation. This is explained by the fact 
that the male-producing and female-producing eggs are already differentiated 
from one another before the time of polar body formation. The eggs which 
will develop into males through the elimination of the double sex chromosome 
are smaller than the female-producing eggs, where there is no elimination. In 
this case, therefore, the elimination of the sex chrqmosome is not a matter of 
chance but is determined by conditions antecedent to the time of polar-body 
formation. Such conditions, therefore, constitute a sex-determining factor in 
the chain of causation of sex. 
So it would seem to be in the case of the domestic fowl. As to the nature of 
these conditions, hardly more than speculative suggestions can be offered, but 
perhaps they will not be less speculative than other theories advanced to account 
for the manner in which sex is determined. 
It would seem that many of the more general statements implying that sex 
determination is readily modified by external conditions and that sex may be 
controlled are not in harmony with all the facts. The approximate equality of 
the sexes is one of the outstanding phenomena among the higher forms which 
reproduce bisexually. But if environmental factors play such a highly significant 
part in the modification of sex determination as is so frequently claimed, is it 
not almost inconceivable that with so many organisms under such varying 
environmental conditions throughout all parts of the world the sexes should 
usually approximate equality? Furthermore, it may be legitimate to inquire 
as to the nature of sex potencies which are assumed to be operative in producing 
.4ex and what causes contribute to the development of different degrees of potency. 
It is now apparent that in some of the experiments designed to test the stability 
of the sex-determining mechanism many of the interpretations based upon the 
results secured require examination. 
A number of factors have been found to be associated with one sex or the other, 
and the results secured in several lines of work would seem to be materially 
weakened by the apparent desire to disregard, in a large measure, the significance 
of the chromosomal mechanism, which is continually receiving stronger and 
stronger support from cytological investigations. It should not be overlooked 
that notwithstanding the laborious procedure and technical difficulties involved 
in conducting cytological investigations remarkable achievements have been 
accomplished in definitely correlating cytological facts with genetic results for an 
ever increasing number of forms. If the different phenomena which have been 
found to be associated with one sex or the other can also be shown to be associated 
with the constitution of the chromosome complex then it would appear that the 
metabolic and chromosome theories can be harmonized and real progress made 
toward a solution of the problem of the causation of sex. 
As far as the chromosome theory of sex is concerned, in view of the variety of 
circumstances under which sex ratios have been modified and the mode of sex 
