Success in Controlling Sex 
the ova, and the retention of this same X in 
the eggs of identical chromosomal constitution 
in the autumn. (2) The elimination of a Y 
chromosome from the other half of the eggs 
laid during the autumn, and the retention of 
of all these same Y’s in the homologous eggs 
laid in the spring. Alternative assumptions to 
(1) and (2) would be that the X’s of eggs laid 
in the spring became Y-like in the presence of 
the sperm from a wide cross, and only then 
become so; and that the Y’s of autumn eggs 
become gradually, in the presence of any kind 
of sperm, more X-like in quality. (3) That 
all other chromosomes than the sex-chromo- 
somes must display no such thing as a seasonal 
preference for ‘‘staying’”’ or ‘‘going,’’ since 
every observable character of the hybrids 
betrays an inheritance from both parents. If 
any one can accept such an incredible hypo- 
thesis of chromosome behavior, he must also 
face this fact: these sex-controlled experiments 
. produce several grades of females. Some are quite 
nearly males, although they lay eggs. Is it too 
hazardous to suggest that in one and the same 
egg the Y could hardly have ‘‘gone out’”’ to 
allow the egg to develop into a female, and 
yet have ‘‘stayed in’’ to deliver the relative 
masculinity which we easily detect and measure 
in this same female? If sex is directly the 
creature of a sex chromosome, the sex situation 
found in some of my female doves requires that 
the male-producing chromosome be eliminated 
from, and retained in, the same egg. In the 
face of these facts, it is wholly absurd to 
postulate a differential maturation as a basis 
for the observed phenomena of these sex- 
series. A true reversal of sex has been effected, 
and the possibilities of its being apparent 
rather than real have been excluded. 
Another line of evidence concerns 
“developmental energy”’ of the spring- 
to-autumn series of eggs of the doves. 
It has already been mentioned that 
under the conditions of these experi- 
ments the last few eggs of the season 
are weak, or fail altogether to hatch. 
These eggs are, however, the largest of 
the entire season. It will be seen that 
those germs that store most materials 
are developmentally the weakest germs. 
When we measure the length of life 
of the birds hatched, we find that the 
smaller eggs of the season, and probably 
too the smaller eggs of the clutch, give 
rise to the longest-lived birds. These 
smaller eggs furnish therefore this addi- 
tional evidence of greater developmental 
energy than is possessed by the larger 
eggs. 
Several hundred chemical analyses— 
each of a single yolk—have shown that 
the size increase of the eggs is accom- 
plished by actual increase of the various 
161 
solids of the egg; and that the increase 
from spring to autumn is gradual; there 
is nowhere any sudden break or varia- 
tion. In connection with the analyses 
it was found that the smaller, spring 
eggs (male-producers) contain more 
water than do the larger, fall eggs 
(female-producers), and a similar rela- 
tion seems to hold between the smaller 
and larger eggs of the clutches, as 
between the larger and smaller of the 
season. That is to say, the higher 
water content accompanies the male- 
producing germ, but the experimental 
procedures during the season carry all 
the yolks gradually to a lower level, and 
then all produce females. 
These various facts are taken by Dr. 
Riddle to mean that the male-produc- 
ing egg has a higher metabolism than 
the female-producing egg. If so, any- 
thing which increased the metabolism 
of an egg, which gave it greater vigor, 
would tend to make it produce a male. 
Now it is well known that crossing 
increases the vigor of offspring. Cross- 
breeding is used by every stock breeder 
to produce vigorous animals, and even 
the farmer sows by preference, cross- 
bred maize, because it yields more 
sturdy plants; so if we suppose that the 
amount of vigor is in proportion to the 
width of the cross, we will understand 
a possible explanation of the fact cited 
at the beginning of this paper, that when 
two distinct families of pigeons are 
crossed a higher metabolism is at once 
established and the offspring are all 
males. 
Another line of available evidence 
relates to the variation in weight of the 
birds themselves at different seasons. 
It is found that at the season when the 
female lays the largest eggs, she herself, 
and also her consort, are smaliest in 
size. 
It has further been found that the 
females hatched from smaller eggs are 
more masculine in their behavior than 
females from larger eggs of the same 
clutch, and that females hatched early 
in the season are more masculine than 
their full sisters hatched late in the 
season. 
The conclusion reached from weigh- 
ing yolks, and from yolk-analyses, is 
