220 
Journal of Agricultural Research v 0 i. xxviii, No. 3 
determination apparently affected, and also in view of the most recent interpreta¬ 
tions concerning the physiological constitution of the chromosomes, with their 
associated interactions, it seems certain that the simple hypothesis of an un¬ 
changeable hereditary entity must be modified. Two views may be expressed as 
follows: The sex chromosome may cause sex, or the presence or absence of the sex 
chromosome may be the effect of the two sexes being produced by differing levels 
of metabolism. At the same time, in the case of the domestic fowl, as in many 
of the other higher forms, the presence or absence of a second sex chromosome 
seems to be 'definitely associated with sex. But it is evident that sex can not 
depend on a chromosome alone, for the chromosome obviously acts by its relation 
with the cell protoplasm. Seemingly the presence of a particular chromosome 
provides only one side of a reciprocal reaction, while the determination of sex 
must depend upon the complete result of all the reciprocal reactions. 
There may not be any heredity other than Mendelian, and although it is evident 
that the chromosomes are responsible for the segregation of Mendelian char¬ 
acters, it has become apparent that the cytoplasm can not be relegated to a posi¬ 
tion of serving as a mediumronly in which the chromosomes carry on their reac¬ 
tions. The chromosomes can not be regarded as acting independently of the 
cytoplasm and in fact there is much evidence of interaction between chromo¬ 
somes and cytoplasm. The coexistence in the primary oocyte of the germinal 
vesicle and the enormous growth of the cell with its formation of reserve food 
material suggests a causal connection between them. The diffusion of chromatin 
in the ordinary resting nucleus has the result of increasing its area in proportion 
to its mass and thus favors active metabolism. Similarly, it has been held that 
the excessive diffusion of chromosomes in the germinal vesicles of many animals 
gives rise to an intense activity of the chromosomes in the elaboration of yolk. 
Finally, it may be said that the interaction which takes place between nucleus 
and cytoplasm is certain to effect a modification in both nucleus and cytoplasm. 
Applying these ideas to the case in hand, it does not seem unreasonable to 
suppose that the nature of the reactions within the nucleus would vary from time 
to time throughout the maturation process.’ Variations in the chemical com¬ 
position of the eggs in relation to increased egg production in the domestic fowl- 
which have been shown to exist, might also exert an influence on the nature of 
interactions between the chromosomes and the cytoplasm. It is quite con¬ 
ceivable, therefore, that during the early period of egg .production a given condi¬ 
tion of reactions might prevail, and this particular condition might be modified as 
egg production increased. This being possible, it is also possible that under a 
given set of conditions certain factors may operate in causing the female-producing 
complex to be extruded more frequently in polar-body formation than the male- 
producing complex, and conversely when the conditions become altered. If 
this be possible, then it is reasonable to suppose that during the early period 
of egg production in the domestic fowl female-producing complexes are extruded 
more frequently than male-producing complexes and that as production increases 
the situation becomes reversed. Finally, since it seems obvious that there are 
more male-producing than female-producing zygotes produced during the early 
period of egg production and that this situation becomes reversed as egg produc¬ 
tion increases, and since it therefore follows that there must, of necessity, be 
differential maturation, this hypothesis has been suggested to account for more 
males than females being produced during the early period of egg production and 
more females than males during the later period of egg production. 
